RS-485 - User contributions [en]

USB

2026-05-03T12:42:39Z

RS-485: Imported from Wikipedia (overwrite)

{{Short description|Standard for computer data connections}}
{{About|the computer bus standard|other uses}}
{{Use American English|date=May 2023}}
{{Use dmy dates|date=May 2023}}
{{cs1 config|mode=cs1|name-list-style=none|display-authors=all}}
{{infobox connector
| name = USB Universal Serial Bus
| type = [[Bus (computing)|Bus]]
| image = [[File:Locale_RS6_USB-C connector and receptacle.webp|frameless|upright=1.3]]
| logo = Certified USB.svg
| caption = [[USB-C]] connector for USB, Thunderbolt, and other protocols (plug and receptacle shown)
| designer = {{plainlist|
* [[Compaq]]
* [[Digital Equipment Corporation|DEC]]
* [[IBM]]
* [[Intel]]
* [[Microsoft]]
* [[NEC]]
* [[Nortel]]
}}
| design_date = {{start date and age |1996|1}}
| production_date = Since May 1996<ref>{{cite web |url=http://download.intel.com/design/intarch/datashts/29055002.pdf |publisher=Intel |title=82371FB (PIIX) and 82371SB (PIIX3) PCI ISA IDE Xcelerator |date=May 1996 |access-date=12 March 2016 |url-status=dead |archive-url=https://web.archive.org/web/20160313120109/http://download.intel.com/design/intarch/datashts/29055002.pdf |archive-date=13 March 2016}}</ref>
| superseded = [[Serial port]], [[parallel port]], [[game port]], [[Apple Desktop Bus]], [[PS/2 port]], and [[FireWire]] (IEEE 1394)
| superseded_by =
| superseded_by_date =
| open = Yes
}}
[[File:USB 80Gbps logo.svg|thumb|USB 80 Gbit/s port logo]]
'''Universal Serial Bus''' ('''USB''') is an [[technical standard|industry standard]], developed by [[USB Implementers Forum]] (USB-IF), for digital data transmission and power delivery between many types of electronics. It specifies the architecture, in particular the physical [[Interface (computing)|interfaces]], and [[communication protocol]]s to and from ''hosts'', such as [[personal computer]]s, to and from [[peripheral]] ''devices'', e.g. displays, keyboards, and mass storage devices, and to and from intermediate ''hubs'', which multiply the number of a host's ports.<ref name=USB42Spec>{{cite web |date=October 2022 |title=USB4 Specification V2.0 |url=https://www.usb.org/document-library/usb4r-specification-v20 |access-date=27 February 2025 |publisher=USB Implementers Forum |format=ZIP |edition=Version 2.0}}</ref>

Introduced in 1996, USB was originally designed to standardize the connection of peripherals to computers, replacing various interfaces such as [[serial port]]s, [[parallel port]]s, [[game port]]s, and [[Apple Desktop Bus]] (ADB) ports.<ref>{{cite web |title=About USB-IF |url=https://www.usb.org/about |access-date=27 April 2023 |publisher=USB Implementers Forum |archive-url=https://web.archive.org/web/20230430175120/https://www.usb.org/about |archive-date=2023-04-30}}</ref> Early versions of USB became commonplace on a wide range of devices, such as keyboards, mice, cameras, printers, scanners, flash drives, smartphones, game consoles, and power banks.<ref>{{Cite news |date=20 May 1999 |title=USB deserves more support |url=http://simson.net/clips/1999/99.Globe.05-20.USB_deserves_more_support+.shtml |url-status=live |archive-url=https://web.archive.org/web/20120406080011/http://simson.net/clips/1999/99.Globe.05-20.USB_deserves_more_support+.shtml |archive-date=6 April 2012 |access-date=12 December 2011 |newspaper=Boston Globe Online |department=Business |publisher=Simson }}</ref> USB has since evolved into a standard to replace virtually all common ports on computers, mobile devices, peripherals, power supplies, and manifold other small electronics.

In the latest standard, the [[USB-C]] connector replaces many types of connectors for power (up to 240 W), displays (e.g. DisplayPort, HDMI), and many other uses, as well as all previous USB connectors.

{{As of|2024|post=,}} USB consists of four generations of specifications: [[#USB 1.x|USB 1.''x'']], [[#USB 2.0|USB 2.0]], [[USB 3.0|USB 3.''x'']], and [[USB4]]. The USB4 specification enhances the data transfer and power delivery functionality with "a connection-oriented tunneling architecture designed to combine multiple protocols onto a single physical interface so that the total speed and performance of the USB4 Fabric can be dynamically shared."<ref name=USB42Spec/> In particular, USB4 supports the tunneling of the [[Thunderbolt (interface)|Thunderbolt 3]] protocols, namely [[PCI Express]] (PCIe, load/store interface) and [[DisplayPort]] (display interface). USB4 also adds host-to-host interfaces.<ref name=USB42Spec/>

Each specification sub-version supports different [[signaling rate]]s from 1.5 and 12 Mbit/s [[Duplex (telecommunications)#Half duplex|half-duplex]] in USB 1.0/1.1 to 80 Gbit/s [[Duplex (telecommunications)#Full duplex|full-duplex]] in USB4 2.0.<ref name=USB31Spec>{{cite web |title=Universal Serial Bus 3.1 Specification |url=https://www.usb.org/sites/default/files/documents/usb_3_1_1_0.zip |access-date=27 April 2023 |publisher=USB Implementers Forum |format=ZIP |date=26 July 2013 |edition=Revision 1.0}}{{Dead link |date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes}}</ref><ref name=USB2Spec>{{cite web |url=https://www.usb.org/sites/default/files/documents/usb_2_0.zip |title=Universal Serial Bus 2.0 Specification |edition=Revision 2.0 |date=27 April 2000 |format=ZIP |publisher=USB Implementers Forum |access-date=27 April 2023 }}{{Dead link|date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref name=USB3211Spec>{{cite web |url=https://www.usb.org/document-library/usb-32-revision-11-june-2022 |publisher=USB Implementers Forum |title=Universal Serial Bus 3.2 Revision 1.1 |date=June 2022 |format=ZIP |edition=Revision 1.1 |access-date=14 April 2024}}</ref><ref name=USB42Spec/> USB also provides power to peripheral devices; the latest versions of the standard extend the power delivery limits for battery charging and devices requiring up to 240 watts as defined in [[USB hardware#USB Power Delivery|USB Power Delivery (USB-PD)]] Rev. 3.1 V1.1 in 2021.<ref name=PDSpec>{{cite web |url=https://www.usb.org/sites/default/files/documents/pd_specification.zip |title=Universal Serial Bus Power Delivery Specification Revision 3.1 Version 1.1 |date=July 2021 |edition=Version 1.1 |format=ZIP |publisher=USB Implementers Forum |access-date=27 April 2023 }}{{Dead link|date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> Over the years, USB(-PD) has been adopted as the standard power supply and charging format for many mobile devices, such as mobile phones, reducing the need for proprietary chargers.<ref>{{cite web |url=http://www.gsmworld.com/newsroom/press-releases/2009/3582.htm |title=Universal Charging Solution |publisher=GSMA |date=17 February 2009 |access-date=12 December 2011 |url-status=live |archive-url=https://web.archive.org/web/20111130092204/http://www.gsmworld.com/newsroom/press-releases/2009/3582.htm |archive-date=30 November 2011}}</ref>

== Overview ==
USB was designed to standardize the connection of [[peripheral]]s to personal computers, both to exchange data and to supply electric power. It has largely replaced interfaces such as [[serial port]]s and [[parallel port]]s and has become commonplace on various devices. Peripherals connected via USB include computer keyboards and mice, video cameras, printers, portable media players, mobile (portable) digital telephones, disk drives, and network adapters.

USB connectors have been increasingly replacing other types of charging cables for portable devices.<ref>{{cite web |url=https://interestingengineering.com/culture/eu-adopts-usb-c-charging-standard |title=Universal charger rule: USB-C becomes mandatory for devices sold in EU |access-date=2025-04-26 |archive-url=https://web.archive.org/web/20260111203900/https://interestingengineering.com/culture/eu-adopts-usb-c-charging-standard |archive-date=2026-01-11}}</ref><ref>{{cite web |url=https://www.theregister.com/2024/10/14/uk_usbc_charging_standard/ |title=UK ponders USB-C as common charging standard |access-date=2025-04-26 |archive-url=https://web.archive.org/web/20260106173332/https://www.theregister.com/2024/10/14/uk_usbc_charging_standard/ |archive-date=2026-01-06}}</ref><ref>{{cite web |url=https://www.hwe.design/design-fundamentals/usb-charging-basics |title=USB Charging |access-date=2025-04-26 |archive-url=https://web.archive.org/web/20260116152257/https://www.hwe.design/design-fundamentals/usb-charging-basics |archive-date=2026-01-16}}</ref>

USB connector interfaces are classified into three types: the many various ''legacy'' Type-A (controlling host) and Type-B (attached device) connectors found on ''hosts'', ''hubs'', and ''peripheral devices'', and the modern Type-C ([[USB-C]]) connector, which replaces the many legacy connectors as the only applicable connector for USB4.

The Type-A and Type-B connectors came in Standard, Mini, and Micro sizes. The standard format was the largest and was mainly used for desktop and larger peripheral equipment. The Mini-USB connectors (Mini-A, Mini-B, Mini-AB) were introduced for mobile devices. Still, they were quickly replaced by the thinner Micro-USB connectors (Micro-A, Micro-B, Micro-AB). The Type-C connector, also known as USB-C, is not exclusive to USB, is the only current standard for USB, is required for USB4, and is required by other standards, including modern DisplayPort and Thunderbolt. It is reversible and can support various functionalities and protocols, including USB; some are mandatory, and many are optional, depending on the type of hardware: host, peripheral device, or hub.<ref>{{cite web |url=https://www.usb.org/sites/default/files/documents/cabconn20.pdf |title=Universal Serial Bus Cables and Connectors Class Document Revision 2.0 |publisher=USB Implementers Forum |access-date=27 April 2023 }}{{Dead link|date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref><ref>{{cite web |url=https://www.usb.org/sites/default/files/documents/usb_type-c_specification_1_0.pdf |title=Universal Serial Bus Type-C Cable and Connector Specification Revision 1.0 |publisher=USB Implementers Forum |access-date=27 April 2023 }}{{Dead link|date=November 2024 |bot=InternetArchiveBot |fix-attempted=yes }}</ref>

USB specifications provide backward compatibility, usually resulting in decreased signaling rates, maximal power offered, and other capabilities. The USB 1.1 specification replaces USB 1.0. The USB 2.0 specification is backward-compatible with USB 1.0/1.1. The USB 3.2 specification replaces USB 3.1 (and USB 3.0) while including the USB 2.0 specification. USB4 "functionally replaces" USB 3.2 while retaining the USB 2.0 bus operating in parallel.<ref name="USB31Spec" /><ref name=USB2Spec/><ref name=USB32101Spec>{{cite web |url=https://www.usb.org/document-library/usb-32-revision-11-june-2022 |title=USB 3.2 Revision 1.01 – June 2022 |edition=Revision 1.01 |date=Oct 2023 |access-date=14 April 2024}}</ref><ref name=USB42Spec/>

The USB 3.0 specification defined a new architecture and protocol named ''SuperSpeed'' (aka ''SuperSpeed USB'', marketed as ''SS''), which included a new lane for a new signal coding scheme (8b/10b symbols, 5 Gbit/s; later also known as ''Gen 1'') providing full-duplex data transfers that physically required five additional wires and pins, while preserving the USB 2.0 architecture and protocols and therefore keeping the original four pins/wires for the USB 2.0 backward-compatibility resulting in 9 wires (with 9 or 10 pins at connector interfaces; ID-pin is not wired) in total.

The USB 3.1 specification introduced an ''Enhanced SuperSpeed System'' – while preserving the ''SuperSpeed'' architecture and protocol (''SuperSpeed USB'') – with an additional ''SuperSpeedPlus'' architecture and protocol (aka ''SuperSpeedPlus USB'') adding a new coding schema (128b/132b symbols, 10 Gbit/s; also known as ''Gen 2''); for some time marketed as ''SuperSpeed+'' (''SS+'').

The USB 3.2 specification<ref name=USB32Spec/> added a second lane to the ''Enhanced SuperSpeed System'' besides other enhancements so that the ''SuperSpeedPlus USB'' system part implements the ''Gen 1×2'', ''Gen 2×1,'' and ''Gen 2×2'' operation modes. However, the ''SuperSpeed USB'' part of the system still implements the one-lane ''Gen 1×1'' operation mode. Therefore, two-lane operations, namely ''USB 3.2 Gen 1×'''2''' ''(10 Gbit/s) and ''Gen 2×'''2''' ''(20 Gbit/s), are only possible with Full-Featured USB-C. As of 2023, they are somewhat rarely implemented; Intel, however, started to include them in its 11th-generation SoC processor models, but Apple never provided them. On the other hand, ''USB 3.2 Gen 1(×1)'' (5 Gbit/s) and ''Gen 2(×1)'' (10 Gbit/s) have been quite common for some years.

===Connector type quick reference===
{{Main|USB hardware#Connectors}}
Each USB connection is made using two connectors: a ''receptacle'' and a ''plug''. Pictures show only receptacles:
{{mw-datatable}}
{| class="wikitable mw-datatable" style="text-align:center; margin-left:auto; margin-right:auto;"
|+ Available connectors by USB standard
|-
! colspan=2|Standard
! [[#1.x|USB 1.0]] 1996
! [[#1.x|USB 1.1]] 1998
! [[#2.0|USB 2.0]] 2000
! USB 2.0 Revised
! [[USB 3.0]] 2008
! [[USB 3.0#3.1|USB 3.1]] 2013
! [[USB 3.0#3.2|USB 3.2]] 2017
! [[USB4]] 2019
! [[USB4#USB4_Version_2.0|USB4 2.0]] 2022
|-
! rowspan="4" | Max Speed
! Recommended marketing since 2022{{R|USBDataPerformance}}
| colspan="2" | '''Basic-Speed''' [[File:Certified USB.svg|40px]]
| rowspan="3" colspan="2" | '''High-Speed''' [[File:Certified Hi-Speed USB.svg|40px]]
| '''USB 5Gbps''' [[File:USB 5Gbps logo.svg|class=skin-invert-image|40px]]
| '''USB 10Gbps''' [[File:USB 10Gbps logo.svg|class=skin-invert-image|40px]]
| '''USB 20Gbps''' [[File:USB 20Gbps logo.svg|class=skin-invert-image|40px]]
| rowspan="2" |'''USB 40Gbps''' [[File:USB 40Gbps logo 01.svg|class=skin-invert-image|40px]]
| rowspan="2" | '''USB 80Gbps''' [[File:USB 80Gbps logo.svg|class=skin-invert-image|40px]]
|-
! Original label
| rowspan="2" colspan="2" | ''Low-Speed & Full-Speed'' [[File:USB icon.svg|class=skin-invert-image|40px]]
| ''SuperSpeed'', or ''SS'' [[File:USB SuperSpeed 5 Gbps Trident Logo.svg|class=skin-invert-image|40px]]
| ''SuperSpeed+'', or ''SS+'' [[File:USB SuperSpeed 10 Gbps Trident Logo.svg|class=skin-invert-image|40px]]
| ''SuperSpeed USB 20Gbps'' [[File:USB SuperSpeed 20 Gbps Trident Logo.svg|class=skin-invert-image|40px]]
|-
! Operation mode
| USB 3.2 Gen 1×1
| USB 3.2 Gen 2×1
| USB 3.2 Gen 2×2
| USB4 Gen 3×2
| USB4 Gen 4×2
|-
! Signaling rate
| colspan="2" | 1.5 Mbit/s & 12 Mbit/s
| colspan="2" | 480 Mbit/s
| 5 Gbit/s
| 10 Gbit/s
| 20 Gbit/s
| 40 Gbit/s
| 80 Gbit/s
|-
! rowspan="9" | Connector
! {{nowrap|Standard-A}}
| colspan="2" | [[File:USB Type-A receptacle White.svg|class=skin-invert-image|75px]]
| colspan="2" | [[File:USB Type-A receptacle Black.svg|class=skin-invert-image|75px]]
| colspan="2" | [[File:USB 3.0 Type-A receptacle blue.svg|class=skin-invert-image|75px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Type-A receptacle blue.svg|50px]]<ref group="rem" name="OLOp">Limited to max speed at 10 Gbit/s, since only one-lane (''×1'') operation mode is possible.</ref>
| colspan="2" rowspan="2" {{N/A}}
|-
! {{nowrap|Standard-B}}
| colspan="4" | [[File:USB Type-B receptacle.svg|class=skin-invert-image|x60px]]
| colspan="2" | [[File:USB 3.0 Type-B receptacle blue.svg|class=skin-invert-image|x75px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Type-B receptacle blue.svg|50px]]<ref group="rem" name="OLOp"/>
|-
! {{nowrap|Mini-A}}
| rowspan="3" |<ref group="rem" name="bc1.1">[[Backward compatibility]] given.</ref>
| colspan="3" | [[File:USB Mini-A receptacle.svg|class=skin-invert-image|67x67px]]
| colspan="5" rowspan="3" {{N/A}}
|-
! {{nowrap|Mini-AB}}<ref group="rem" name="RecOnly">Only as receptacle.</ref><ref group="rem">Accepts both Mini-A and Mini-B plugs.</ref>
| colspan="3" | [[File:USB_Mini-AB_receptacle.svg|class=skin-invert-image|75x75px]]
|-
! {{nowrap|Mini-B}}
| colspan="3" | [[File:USB Mini-B receptacle.svg|class=skin-invert-image|67x67px]]
|-
! {{nowrap|Micro-A}}<ref group="rem" name="PlugOnly">Only as plug.</ref>
| colspan="3" rowspan="3" | <ref group="rem" name="bc1.1"/><ref group="rem" name="bc2"/>
| [[File:USB Micro-A.svg|class=skin-invert-image|alt=|frameless|75x75px]]
| colspan="2" | [[File:USB 3.0 Micro-A.svg|class=skin-invert-image|frameless|117x117px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Micro-A.svg|60px]]<ref group="rem" name="OLOp"/>
| colspan="2" rowspan="3" {{N/A}}
|-
! {{nowrap|Micro-AB}}<ref group="rem" name="RecOnly"/><ref group="rem">Accepts both Micro-A and Micro-B plugs.</ref>
| [[File:USB Micro-AB receptacle.svg|class=skin-invert-image|75x75px]]
| colspan="2" | [[File:USB micro AB SuperSpeed.svg|class=skin-invert-image|frameless|117x117px]]
| style="background:#FEE4BA" | [[File:USB micro AB SuperSpeed.svg|60px]]<ref group="rem" name="OLOp"/>
|-
! {{nowrap|Micro-B}}
| [[File:USB Micro B receptacle pinout.svg|class=skin-invert-image|alt=|frameless|75x75px]]
| colspan="2" | [[File:USB 3.0 Micro-B receptacle.svg|class=skin-invert-image|frameless|117x117px]]
| style="background:#FEE4BA" | [[File:USB 3.0 Micro-B receptacle.svg|60px]]<ref group="rem" name="OLOp"/>
|-
! {{nowrap|Type-C}} {{nowrap|(USB-C)}}
| colspan="3" |<ref group="rem" name="bc2">Backward compatibility given by USB 2.0 implementation.</ref>
| colspan="6" style="font-size:60%"| [[File:USB Type-C Receptacle Pinout.svg|class=skin-invert-image|117x117px]] (Enlarged to show detail)
|-
| ''Remarks:''
| scope=col colspan=10 | {{reflist|group="rem"}}
|}

=== Objectives ===
The Universal Serial Bus was developed to simplify and improve the interface between personal computers and peripheral devices, such as cell phones, computer accessories, and monitors, when compared with previously existing standard or ''ad hoc'' proprietary interfaces.<ref name="JA2015">Axelson, Jan (2015). ''USB Complete: The Developer's Guide, Fifth Edition'', Lakeview Research LLC, {{ISBN|1931448280}}, pp. 1–7.</ref>

From the computer user's perspective, the USB interface improves ease of use in several ways:
* The USB interface is self-configuring, eliminating the need for the user to adjust the device's settings for speed or data format, or configure [[interrupt]]s, input/output addresses, or direct memory access channels.<ref>{{cite web |website=PC |url=https://www.pcmag.com/encyclopedia/term/44434/how-to-install-a-pc-peripheral |title=Definition of: how to install a PC peripheral |publisher=[[Ziff Davis]] |access-date=17 February 2018 |archive-date=22 March 2018 |archive-url=https://web.archive.org/web/20180322020256/https://www.pcmag.com/encyclopedia/term/44434/how-to-install-a-pc-peripheral |url-status=live}}</ref>
* USB connectors are standardized at the host, so any peripheral can use most available receptacles.
* USB takes full advantage of the additional processing power that can be economically put into peripheral devices so that they can manage themselves. As such, USB devices often do not have user-adjustable interface settings.
* The USB interface is [[hot-swappable]] (devices can be exchanged without shutting the host computer down).
* Small devices can be powered directly from the USB interface, eliminating the need for additional power supply cables.
* Because the use of the USB logo is only permitted after [[compliance testing]], the user can have confidence that a USB device will work as expected without extensive interaction with settings and configuration.
* The USB interface defines protocols for recovery from common errors, improving reliability over previous interfaces.<ref name="JA2015"/>
* Installing a device that relies on the USB standard requires minimal operator action. When a user plugs a device into a port on a running computer, either it entirely automatically configures using existing [[device driver]]s or the system prompts the user to locate a driver, which it then installs and configures automatically.

The USB standard also provides multiple benefits for hardware manufacturers and software developers, specifically in the relative ease of implementation:
* The USB standard eliminates the requirement to develop proprietary interfaces to new peripherals.
* The wide range of transfer speeds available from a USB interface suits devices ranging from keyboards and mice up to streaming video interfaces.
* A USB interface can be designed to provide the best available [[Latency (engineering)|latency]] for time-critical functions or can be set up to do background transfers of bulk data with little impact on system resources.
* The USB interface is generalized with no signal lines dedicated to only one function of one device.<ref name="JA2015"/>

===Limitations===
As with all standards, USB possesses multiple limitations to its design:
* USB cables are limited in length, as the standard was intended for peripherals on the same tabletop, not between rooms or buildings. However, a USB port can be connected to a [[Gateway (telecommunications)|gateway]] that accesses distant devices.
* USB data transfer rates are slower than those of other interconnects (e.g., ethernet) released in the same timeframe.
* USB has a strict [[tree network]] topology and [[Master–slave (technology)|master/slave]] protocol for addressing peripheral devices; slave devices cannot interact with one another except via the host, and two hosts cannot communicate over their USB ports directly. Some extension to this limitation is possible through [[USB On-The-Go]], Dual-Role-Devices<ref>{{cite web |url=https://blogs.synopsys.com/tousbornottousb/2018/05/03/usb-dual-role-replaces-usb-on-the-go/ |title=To USB or Not to USB: USB Dual Role replaces USB On-The-Go |last=Huang |first=Eric |work=synopsys.com |date=3 May 2018 |access-date=21 July 2021 |archive-date=25 July 2021 |archive-url=https://web.archive.org/web/20210725064610/https://blogs.synopsys.com/tousbornottousb/2018/05/03/usb-dual-role-replaces-usb-on-the-go/ |url-status=live}}</ref> and [[protocol bridge]].
* A host cannot broadcast signals to all peripherals at once; each must be addressed individually.
* While converters exist between certain [[Legacy system|legacy interfaces]] and USB, they might not provide a full implementation of the legacy hardware. For example, a USB-to-parallel-port converter might work well with a printer, but not with a scanner that requires bidirectional use of the data pins.

For a product developer, using USB requires the implementation of a complex protocol and implies an "intelligent" controller in the peripheral device. Developers of USB devices intended for public sale generally must obtain a USB ID, which requires that they pay a fee to the [[USB Implementers Forum]] (USB-IF). Developers of products that use the USB specification must sign an agreement with the USB-IF. Use of the USB logos on the product requires annual fees and membership in the organization.<ref name="JA2015"/>

== History ==
[[File:USB Icon.svg|thumb|upright=0.5|alt=Large circle is left end of horizontal line. The line forks into three branches ending in circle, triangle and square symbols.|The basic USB ''trident'' logo<ref>{{cite web | title = Icon design recommendation for Identifying USB 2.0 Ports on PCs, Hosts and Hubs | publisher = USB Implementers Forum | url = http://www.usb.org/developers/docs/icon_design.pdf | access-date = 26 April 2013 | archive-date = 3 October 2016 | archive-url = https://web.archive.org/web/20161003080319/http://www.usb.org/developers/docs/icon_design.pdf | url-status = live}}.</ref>]]

A group of seven companies began the development of USB in 1995:<ref>{{cite web |url=https://www.usb.org/members |title=Members |access-date=7 November 2021 |archive-date=7 November 2021 |archive-url=https://web.archive.org/web/20211107220855/https://www.usb.org/members |url-status=live}}</ref> [[Compaq]], [[Digital Equipment Corporation|DEC]], [[IBM]], [[Intel]], [[Microsoft]], [[NEC]], and [[Nortel]]. The goal was to make it fundamentally easier to connect external devices to PCs by replacing the multitude of connectors at the back of PCs, addressing the usability issues of existing interfaces, and simplifying software configuration of all devices connected to USB, as well as permitting greater data transfer rates for external devices and [[plug and play]] features.<ref>{{cite web|url=https://www.intel.com/content/www/us/en/standards/usb-two-decades-of-plug-and-play-article.html|title=Two decades of "plug and play": How USB became the most successful interface in the history of computing|access-date=14 June 2021|archive-date=15 June 2021|archive-url=https://web.archive.org/web/20210615025638/https://www.intel.com/content/www/us/en/standards/usb-two-decades-of-plug-and-play-article.html|url-status=live}}</ref> Concepts of the 1979 [[Atari SIO]] serial bus, of the 8-bit Atari computers, and the 1980 [[IEEE-488]] derived [[Commodore bus]], and Hewlett Packard's [[HP-IL]] bus pioneered this approach.<ref>{{cite news|last1=Stilphen|first1=Scott|title=DP Interviews ... Joe Decuir|url=http://www.digitpress.com/library/interviews/interview_joe_decuir.html|access-date=2 August 2017|publisher=Digit Press |archive-url=https://web.archive.org/web/20250603042832/https://www.digitpress.com/library/interviews/interview_joe_decuir.html |archive-date=2025-06-03}}</ref><ref name=":Decuir2023">{{Cite web |last=Decuir |first=Joseph |date=Feb 2023 |title=IEEE – Three generations of animation machines: Atari and Amiga, Joe Decuir, IEEE Fellow UW Engineering faculty |url=https://vcfed.org/wp-content/uploads/2024/02/Joe_Decuir_VCF_West_2023_Slides.pdf |website=VCF – Vintage Computer Foundation}}</ref> A consortium led by Apple, and containing Sony, Panasonic (Matsushita), LG, Toshiba, Hitachi, Cannon, Philips Electronics, Compaq, Thomson and Texas Instruments, would develop the concept further, from 1986, as the [[IEEE 1394]] firewire standard and patent pool.<ref>{{Cite web |title=The Mac Observer – Apple, Sony, Phillips, Others Band Together On FireWire Patent Pool |url=https://www.macobserver.com/news/99/february/990217/firewirealliance.html |access-date=2025-02-10 |website=www.macobserver.com |archive-date=17 February 2025 |archive-url=https://web.archive.org/web/20250217060739/https://www.macobserver.com/news/99/february/990217/firewirealliance.html |url-status=dead }}</ref> [[Joseph C. Decuir]], originally of Atari, then Commodore, and a designer of the Atari SIO common bus, would work on the USB project for Microsoft, obtaining one of the related US patents.<ref>{{Cite patent|number=US5781028A|title=System and method for a switched data bus termination|gdate=1998-07-14|invent1=Decuir|inventor1-first=Joseph C.|url=https://patents.google.com/patent/US5781028A/en?inventor=Joseph+C.+Decuir}}.</ref> [[Ajay Bhatt]] and his team<ref group=note>Bhatt's team at Intel included Bala Sudarshan Cadambi, Jeff Morriss, Shaun Knoll, and Shelagh Callahan.{{cite web |url=https://www.allaboutcircuits.com/news/king-of-plug-and-play-how-usb-took-the-world-by-storm/ |author=Biljana Ognenova |date=2022-02-22 |title=The King of Plug-and-Play: How USB Took the World by Storm |website=allaboutcircuits.com|access-date=2025-04-01}}</ref> worked on the standard at Intel;<ref>{{cite web | url = http://www.intel.com/pressroom/kits/bios/abhatt.htm | title = Intel Fellow: Ajay V. Bhatt | publisher = [[Intel Corporation]] | url-status=dead | archive-url = https://web.archive.org/web/20091104041719/http://www.intel.com/pressroom/kits/bios/abhatt.htm | archive-date = 4 November 2009}}</ref><ref>{{cite web |url= http://www.oregonlive.com/business/index.ssf/2009/05/intel_ad_campaign_remakes_rese.html |title= Intel ad campaign remakes researchers into rock stars |first= Mark |last= Rogoway |work= [[The Oregonian]] |date= 9 May 2009 |access-date= 23 September 2009 |url-status=live |archive-url= https://web.archive.org/web/20090826081315/http://www.oregonlive.com/business/index.ssf/2009/05/intel_ad_campaign_remakes_rese.html |archive-date= 26 August 2009}}</ref> the first [[integrated circuit]]s supporting USB were produced by Intel in 1995.<ref name="1394_2_4">{{cite book |editor-first = Hui |editor1-last = Pan |editor2-first = Paul |editor2-last = Polishuk |title = 1394 Monthly Newsletter |url = https://books.google.com/books?id=fRvbxgH4wmsC&pg=PA7 |access-date = 23 October 2012 |publisher = Information Gatekeepers |pages = 7–9 |id = GGKEY:H5S2XNXNH99 |url-status=live |archive-url = https://web.archive.org/web/20121112184629/http://books.google.com/books?id=fRvbxgH4wmsC&pg=PA7 |archive-date = 12 November 2012}}</ref>

=== USB 1.''x'' ===
[[File:Certified USB.svg|thumb|upright=0.5|The Basic-Speed USB logo]]
Released in January 1996, USB 1.0 specified signaling rates of 1.5 Mbit/s (''Low Bandwidth'' or ''Low Speed'') and 12 Mbit/s (''Full Speed'').<ref>{{cite tech report | title=Universal Serial Bus Specification | number=v1.0 | year=1996 | section=4.2.1 | page=29 | url=https://fl.hw.cz/docs/usb/usb10doc.pdf | url-status=live | archive-url=https://web.archive.org/web/20180130144424/https://fl.hw.cz/docs/usb/usb10doc.pdf | archive-date=30 January 2018}}</ref> It did not allow for extension cables, due to timing and power limitations. Few USB devices made it to the market until USB 1.1 was released in August 1998. USB 1.1 was the earliest revision that was widely adopted and led to what Microsoft designated the "[[Legacy-free PC]]".<ref name="Macworld iMac">{{cite web |url=http://www.macworld.com/article/135017/2008/08/imacanniversary.html |title=Eight ways the iMac changed computing |work=Macworld |date=15 August 2008 |access-date=5 September 2017 |url-status=live |archive-url=https://web.archive.org/web/20111222091746/http://www.macworld.com/article/135017/2008/08/imacanniversary.html |archive-date=22 December 2011 }}</ref><ref name="BusinessWeek iMac">{{cite web | work = Business week | year = 1999 | url = http://www.businessweek.com/1999/99_50/c3659057.htm | title = The PC Follows iMac's Lead | url-status=dead | archive-url = https://web.archive.org/web/20150923221417/http://www.businessweek.com/1999/99_50/c3659057.htm | archive-date = 23 September 2015}}</ref><ref name="Popular Mechanics iMac">{{cite journal|title=Popular Mechanics: Making Connections|journal = Popular Mechanics Magazine|url=https://books.google.com/books?id=R9MDAAAAMBAJ&pg=PA59|date=February 2001|publisher=Hearst Magazines|page=59|issn=0032-4558|url-status=live|archive-url=https://web.archive.org/web/20170215084550/https://books.google.com/books?id=R9MDAAAAMBAJ&pg=PA59|archive-date=15 February 2017}}</ref>

Neither USB 1.0 nor 1.1 specified a design for any connector smaller than the standard type A or type B. Though many designs for a miniaturized type B connector appeared on many peripherals, conformity to the USB 1.''x'' standard was hampered by treating peripherals that had miniature connectors as though they had a tethered connection (that is: no plug or receptacle at the peripheral end). There was no known miniature type A connector until USB 2.0 (revision 1.01) introduced one.

=== USB 2.0 ===
[[File:Certified Hi-Speed USB.svg|thumb|upright=0.5|The Hi-Speed USB logo]]

USB 2.0 was released in April 2000, adding a higher maximum signaling rate of 480 Mbit/s (maximum theoretical data throughput 53 MByte/s<ref name="throughput2.0">{{cite web |url= https://microchipdeveloper.com/usb:high-speed |title= High Speed USB Maximum Theoretical Throughput |date= 23 March 2021 | publisher= Microchip Technology Incorporated |url-status=live |archive-url= https://web.archive.org/web/20210326115716/https://microchipdeveloper.com/usb:high-speed |archive-date= 26 March 2021 | access-date=23 March 2021}}</ref>) named ''High Speed'' or ''High Bandwidth'', in addition to the USB 1.''x'' ''Full Speed'' signaling rate of 12 Mbit/s (maximum theoretical data throughput 1.2 MByte/s).<ref name="throughput1.1">{{cite web |url= https://microchipdeveloper.com/usb:full-speed |title= Full Speed USB Maximum Theoretical Throughput |date= 23 March 2021 | publisher= Microchip Technology Incorporated |url-status=live |archive-url= https://web.archive.org/web/20210326115653/https://microchipdeveloper.com/usb:full-speed |archive-date= 26 March 2021 | access-date=23 March 2021}}</ref>

Modifications to the USB specification have been made via [[Engineering change order|engineering change notices]] (ECNs). The most important of these ECNs are included into the USB 2.0 specification package available from USB.org:<ref>{{cite web |url= http://www.usb.org/developers/docs/usb20_docs/ |title= USB 2.0 Specification |publisher= USB Implementers Forum |url-status=dead |archive-url= https://web.archive.org/web/20171203144114/http://www.usb.org/developers/docs/usb20_docs/ |archive-date= 3 December 2017 |access-date=28 April 2019 }}</ref>

* ''Mini-A and Mini-B Connector''
* ''Micro-USB Cables and Connectors Specification 1.01''
* ''[[InterChip USB]] Supplement''
* ''On-The-Go Supplement 1.3'' [[USB On-The-Go]] makes it possible for two USB devices to communicate with each other without requiring a separate USB host
* ''[[USB hardware#USB battery charging|Battery Charging]] Specification 1.1'' Added support for dedicated chargers, host chargers behavior for devices with dead batteries
* ''Battery Charging Specification 1.2'':<ref name="battchargespec1.2">{{cite web |url=http://www.usb.org/developers/docs/devclass_docs/BCv1.2_070312.zip |title=Battery Charging v1.2 Spec and Adopters Agreement |date=7 March 2012 |publisher=USB Implementers Forum |format=ZIP |url-status=live |archive-url=https://web.archive.org/web/20141006113700/http://www.usb.org/developers/docs/devclass_docs/BCv1.2_070312.zip |archive-date=6 October 2014 |access-date=13 May 2021 }}</ref> with increased current of 1.5 A on charging ports for unconfigured devices, allowing high-speed communication while having a current up to 1.5 A
* ''Link Power Management Addendum ECN'', which adds a ''sleep'' power state

=== USB 3.''x'' ===
{{Main|USB 3.0}}
[[File:Certified SuperSpeed USB Logo.svg|thumb|upright=0.5|Deprecated SuperSpeed USB logo]]

The USB 3.0 specification was released on 12 November 2008, with its management transferring from USB 3.0 Promoter Group to the USB Implementers Forum (USB-IF) and announced on 17 November 2008 at the SuperSpeed USB Developers Conference.<ref name="ReferenceA">{{Cite press release |url=http://www.usb.org/press/USB-IF_Press_Releases/2008_11_17_USB_IF.pdf|title=USB 3.0 Specification Now Available|location=San Jose, California|website=USB Implementers Forum|date=17 November 2008|access-date=22 June 2010|archive-url=https://web.archive.org/web/20100331035202/http://www.usb.org/press/USB-IF_Press_Releases/2008_11_17_USB_IF.pdf|archive-date=31 March 2010}}</ref>

USB 3.0 adds a new architecture and protocol named ''SuperSpeed'', with associated [[backward-compatible]] plugs, receptacles, and cables. SuperSpeed plugs and receptacles are identified with a distinct logo and blue inserts in standard format receptacles.

The SuperSpeed architecture provides for an operation mode at a rate of 5.0 Gbit/s, in addition to the three existing operation modes. Its efficiency is dependent on a number of factors including physical symbol encoding and link-level overhead. At a 5 Gbit/s signaling rate with [[8b/10b encoding]], each byte needs 10 bits to transmit, so the raw throughput is 500 MB/s. When flow control, packet framing and protocol overhead are considered, it is realistic for about two-thirds of the raw throughput, or 330 MB/s to transmit to an application.<ref name=USB30Spec/>{{rp|at=4–19}} SuperSpeed's architecture is [[full-duplex]]; all earlier implementations, USB 1.0-2.0, are half-duplex, arbitrated by the host.<ref>{{cite web |url=http://www8.hp.com/h20195/v2/GetDocument.aspx?docname=4AA4-2724ENW |title=USB 3.0 Technology |year=2012 |access-date=2 January 2014 |publisher=[[Hewlett-Packard|HP]] |format=PDF |url-status=live |archive-url=https://web.archive.org/web/20150219151039/http://www8.hp.com/h20195/v2/GetDocument.aspx?docname=4AA4-2724ENW |archive-date=19 February 2015}}</ref>

Low-power and high-power devices remain operational with this standard, but devices implementing SuperSpeed can provide an increased current of between 150 mA and 900 mA, by discrete steps of 150 mA.<ref name=USB30Spec/>{{rp|at=9–9}}

USB 3.0 also introduced the [[USB Attached SCSI|USB Attached SCSI Protocol (UASP)]], which provides generally faster transfer speeds than the BOT (Bulk-Only-Transfer) protocol.

[[USB 3.1]] specification,<ref name=USB31Spec/> released in July 2013. Firstly, it preserves USB 3.0's ''SuperSpeed'' architecture and protocol and its operation mode is newly named ''USB 3.1 Gen 1'' (previously called ''USB 3.0'' and later marketed as ''USB 5Gbps'' in 2023)<ref name="USB 3.1 language usage 2015-05">{{cite web |date= 2015-05-28|title=USB 3.1 Specification Language Usage Guidelines from USB-IF |url=http://www.usb.org/developers/ssusb/USB_3_1_Language_Product_and_Packaging_Guidelines_FINAL.pdf |publisher = USB Implementers Forum |url-status=dead |archive-url=https://web.archive.org/web/20160312135950/http://www.usb.org/developers/ssusb/USB_3_1_Language_Product_and_Packaging_Guidelines_FINAL.pdf |archive-date=12 March 2016 }}</ref>
<ref name="USB 3.1 language usage 2018-08">{{cite web |author=|date=2018-08-27 |title=USB 3.1 Specification Language Usage Guidelines from USB-IF |url=https://www.usb.org/sites/default/files/usb_3_1_language_product_and_packaging_guidelines_final_0.pdf |publisher=USB Implementers Forum |url-status=live |archive-url=https://web.archive.org/web/20190625163256/https://www.usb.org/sites/default/files/usb_3_1_language_product_and_packaging_guidelines_final_0.pdf|archive-date = 2019-06-25
|access-date=2025-04-02}}</ref><ref>{{cite web |url=https://www.msi.com/blog/usb-3-1-gen1-gen2-explained |title=USB 3.1 Gen 1 & Gen 2 explained |author=Silvia |website=www.msi.org |date=5 August 2015 |access-date=5 April 2018 |archive-date=8 July 2018 |archive-url=https://web.archive.org/web/20180708020201/https://www.msi.com/blog/usb-3-1-gen1-gen2-explained |url-status=live }}</ref> Secondly, it introduces a distinctively new ''SuperSpeedPlus'' architecture and protocol with a second operation mode named as ''USB 3.1 Gen 2''. This doubles the maximum signaling rate to 10 Gbit/s (now marketed as ''USB 10Gbps''), while reducing [[line encoding]] overhead to just 3% by changing the scheme to [[128b/132b]].<ref name="USB 3.1 language usage 2015-05"/><ref>{{cite web |url=http://www.usb.org/developers/docs/usb_31_102214.zip |archive-url=https://web.archive.org/web/20141121225502/http://www.usb.org/developers/docs/usb_31_102214.zip |title=Universal Serial Bus 3.1 Specification |publisher=USB Implementers Forum |date=26 July 2013 |access-date=19 November 2014 |archive-date=21 November 2014 |via=Usb.org |format=ZIP}}</ref>

[[USB 3.2]] specification, released in September 2017,<ref name=USB32Spec>{{Cite web |url=https://www.usb.org/document-library/usb-32-specification-released-september-22-2017-and-ecns |title=The USB 3.2 Specification released on September 22, 2017 and ECNs |date=22 September 2017 |website=usb.org |access-date=4 September 2019 |archive-date=6 July 2019 |archive-url=https://web.archive.org/web/20190706231129/https://www.usb.org/document-library/usb-32-specification-released-september-22-2017-and-ecns|url-status=live}}</ref> preserves existing ''SuperSpeed'' and ''SuperSpeedPlus'' architectures and protocols and their respective operation modes, but introduces two additional ''SuperSpeedPlus'' operation modes (''USB 3.2 Gen 1×2'' and ''USB 3.2 Gen 2×2'') with signaling rates of 10 and 20 Gbit/s (raw data rates of 1212 and 2424 MB/s), respectively. The increased bandwidth is a result of two-lane operation over the additional wires included in all Full-Featured USB‑C Fabrics (all involved devices, hubs, cables and host).<ref>{{Cite press release |url=http://www.usb.org/press/USB_3.2_PR_USB-IF_Final.pdf |title=USB 3.0 Promoter Group Announces USB 3.2 Update |date=25 July 2017 | website = USB Implementers Forum |location=Beaverton, Oregon, US |access-date=27 July 2017 |archive-date=21 September 2017 |archive-url=https://web.archive.org/web/20170921191940/http://www.usb.org/press/USB_3.2_PR_USB-IF_Final.pdf |url-status=live}}</ref>

==== Naming scheme ====
Starting with the USB 3.2 specification, USB-IF introduced a new naming scheme.<ref name="USB 3.2 language usage 2018-10">{{Cite web|url=https://www.usb.org/sites/default/files/usb_3_2_language_product_and_packaging_guidelines_final.pdf |title=USB 3.2 Specification Language Usage Guidelines from USB-IF|date=3 Oct 2018 |website= USB Implementers Forum|url-status=live |access-date=4 September 2019 |archive-date=3 November 2021|archive-url=https://web.archive.org/web/20211103022718/https://www.usb.org/sites/default/files/usb_3_2_language_product_and_packaging_guidelines_final.pdf}}</ref> To help companies with the branding of the different operation modes, USB-IF recommended branding the 5, 10, and 20 Gbit/s capabilities as ''SuperSpeed USB 5Gbps'', ''SuperSpeed USB 10Gbps'', and ''SuperSpeed USB 20Gbps'', respectively.<ref>{{Cite web|last=Ravencraft|first=Jeff|url=https://www.usb.org/sites/default/files/D1T2-1%20-%20USB%20Branding%20Session.pdf|title=USB DevDays 2019 – Branding Session|date=19 November 2019|website=USB Implementers Forum|pages=16|type=Presentation|access-date=22 March 2020|archive-url=https://web.archive.org/web/20200322121822/https://www.usb.org/sites/default/files/D1T2-1%20-%20USB%20Branding%20Session.pdf|archive-date=22 March 2020}}</ref>

In 2023, they were replaced again,<ref name="USB data performance language usage 2024-01">{{cite web |date=22 Jan 2024 |title=USB Data Performance Language Usage Guidelines from USB-IF |url=https://www.usb.org/sites/default/files/usb_data_performance_language_usage_guidelines_jan_2024.pdf |website=USB Implementers Forum |url-status=live |archive-url=https://web.archive.org/web/20241126185424/https://www.usb.org/sites/default/files/usb_data_performance_language_usage_guidelines_jan_2024.pdf |archive-date=2024-11-26 |access-date=2025-04-02}}</ref> removing ''"SuperSpeed"'', with ''USB 5Gbps'', ''USB 10Gbps'', and ''USB 20Gbps''. With new ''Packaging'' and ''Port'' logos.<ref name="USB licensed marks">{{cite web |date=September 20, 2023 |title=USB-IF Licensed Mark(s) Requirements |url=https://www.usb.org/sites/default/files/trademark_license_agreement_licensed_mark_requirements_final_as_of_september_20_2023.pdf |website=USB Implementers Forum |url-status=live |archive-url=https://web.archive.org/web/20250311155445/https://www.usb.org/sites/default/files/trademark_license_agreement_licensed_mark_requirements_final_as_of_september_20_2023.pdf |archive-date=2025-03-11 |access-date=2025-04-02}}</ref>

=== USB4===
{{Update|section|date=August 2024|reason=Incomplete, erroneous and not up-to-date; e.g. lacks differences between USB4 first version and 2.0. Applies also to main article}}
{{main|USB4}}The '''USB4''' specification (Version 1.0) was released on 29 August 2019. It is based on the [[Thunderbolt 3]] protocol, defines 20 and 40 Gbit/s modes over [[USB-C]], and allows tunneling of [[USB 3.2]], [[USB 2.0]], [[PCI Express|PCIe]] and [[DisplayPort]] protocols; Thunderbolt 3 compatibility is optional for USB4 hosts/devices.<ref name="USB4v12">{{cite web |date=March 4, 2019 |title=USB Promoter Group Announces USB4 Specification |url= https://usb.org/sites/default/files/2019-03/USB_PG_USB4_DevUpdate_Announcement_FINAL_20190226.pdf |publisher= USB Promoter Group / USB-IF }}</ref>[[File:Certified USB4 40Gbps Logo.svg|thumb|upright=0.5|Deprecated ''Certified USB4'' logo]]'''USB4 Version 2.0''' (announced 1 September 2022) adds a new physical layer and higher data rates: up to '''80 Gbit/s''' bidirectional, and an asymmetric mode supporting '''120/40 Gbit/s''' (host→device / device→host) for video-heavy use cases. It achieves this using [[Pulse-amplitude modulation|PAM3]] signaling and, in many cases, existing passive “40 Gbit/s” USB-C cables; a new 80 Gbit/s active cable category is also defined. Version 2.0 updates tunneling to align with [[DisplayPort|DisplayPort 2.1]] and [[PCI Express|PCIe 4.0]], and maintains backward compatibility with USB4 1.0, USB 3.2/2.0, and Thunderbolt 3.<ref name="USB4v22">{{cite web |date=September 1, 2022 |title=USB Promoter Group Announces USB4® Version 2.0 (80 Gbps) |url=https://www.usb.org/sites/default/files/2022-09/USB%20PG%20USB4%20Version%202.0%2080Gbps%20Announcement_FINAL.pdf |publisher= USB-IF }}</ref><ref name= "USB802">{{cite web |date=October 18, 2022 |title= USB-IF Announces Publication of New USB4® Specification Enabling USB 80Gbps Performance |url=https://usb.org/sites/default/files/2022-10/USB-IF%20USB%2080Gbps%20Announcement_FINAL_v2.pdf |publisher=USB-IF }}</ref>

Since 2023, the USB-IF recommends consumer-facing product names that reflect link speed (e.g., '''USB 40Gbps''', '''USB 80Gbps'''), replacing “USB4 v1/v2” in marketing and certification listings.<ref name="Naming2">{{cite web |date= January 12, 2023 |title= USB-IF Integrators List Marketing Name Guidance |url= https://www.usb.org/sites/default/files/usb-if_integrators_list_marketing_name_guidance_january_2023.pdf |publisher=USB-IF }}</ref>{{clear}}
{| class="wikitable"
|-
! rowspan="2" style="width:240px" | Connection
! colspan="3" | Mandatory for
! rowspan="2" | Remarks
|-
! style="width:50px; text-align:center"| host !! style="width:50px; text-align:center"| hub !! style="width:50px; text-align:center"| device
|-
| '''USB 2.0''' (480 Mbit/s)|| {{yes}} || {{yes}} || {{yes}} || Contrary to other functions – which use the multiplexing of high-speed links – USB 2.0 over USB-C utilizes its own differential pair of wires.
|-
| '''Tunneled USB 3.2 Gen 2×1''' (10 Gbit/s)|| {{yes}} || {{yes}} || {{no}} ||
|-
| '''Tunneled USB 3.2 Gen 2×2''' (20 Gbit/s)|| {{no}} || {{no}} || {{no}} ||
|-
| '''Tunneled USB 3 Gen T''' (5–80 Gbit/s)|| {{no}} || {{no}} || {{no}} || A type of USB 3 Tunneling architecture where the Enhanced SuperSpeed System is extended to allow operation at the maximum bandwidth available on the USB4 Link.
|-
| '''USB4 Gen 2''' (10 or 20 Gbit/s) || {{yes}} || {{yes}} || {{yes}} || rowspan="2"| Either one or two lanes
|-
| '''USB4 Gen 3''' (20 or 40 Gbit/s) || {{no}} || {{yes}} || {{no}}
|-
| '''Tunneled DisplayPort 1.4a''' || {{yes}} || {{yes}} || {{no}} ||The specification requires that hosts and hubs support the DisplayPort Alternate Mode.
|-
| '''Tunneled PCI Express 3.0''' || {{no}} || {{yes}} || {{no}} || The PCI Express function of USB4 replicates the functionality of previous versions of the [[Thunderbolt (interface)|Thunderbolt]] specification.
|-
| '''Host-to-Host communications''' || {{yes}} || {{yes}} || {{n/a}} || A LAN-like connection between two peers
|-
| '''Thunderbolt 3 Alternate Mode''' || {{no}} || {{yes}} || {{no}} || Thunderbolt 3 uses cables with USB‑C plugs; the USB4 specification allows hosts and devices, and requires hubs, to support interoperability with the standard using the Thunderbolt 3 Alternate Mode (namely DisplayPort and PCIe).
|-
| '''Other Alternate Modes'''|| {{no}} || {{no}} || {{no}}
| USB4 products may optionally offer interoperability with the [[HDMI]], [[Mobile High-Definition Link|MHL]], and [[VirtualLink]] Alternate Modes.
|}

==== September 2022 naming scheme ====
[[File:USB 2022 September naming scheme.svg|thumb|upright=2.8|An overview of USB naming scheme that was put in place in September 2022
 (A mix of USB specifications and their marketing names are being displayed because specifications are sometimes wrongly used as marketing names.){{Disputed inline|File:USB 2022 September naming scheme.svg|for= USB4 20 Gbit/s does not exist; USB4 2×2 is not interchangeable with USB 3.2 2×2 as indicated by the logo; logos for USB 3.x and USB4 are different.|date=July 2023}}]]
Because of the previous confusing naming schemes, USB-IF decided to change it once again. As of 2 September 2022, marketing names follow the syntax "USB ''x''Gbps", where ''x'' is the speed of transfer in Gbit/s.<ref name= "USB data performance language usage 2022-09">{{Cite web |title= USB Data Performance Language Usage Guidelines from USB-IF |url= https://usb.org/sites/default/files/usb_data_performance_language_usage_guidelines_september_2022.pdf|website = USB Implementers Forum | access-date=2 September 2022|archive-date=1 October 2022|archive-url= https://web.archive.org/web/20221001115816/https://www.usb.org/sites/default/files/usb_data_performance_language_usage_guidelines_september_2022.pdf |url-status=dead}}</ref> Overview of the updated names and logos can be seen in the adjacent table.

The operation modes USB 3.2 Gen 2×2 and USB4 Gen 2×2 – or: USB 3.2 Gen 2×1 and USB4 Gen 2×1 – are not interchangeable or compatible; all participating controllers must operate with the same mode.

=== Version histories ===

==== Specification history ====
{| class="wikitable sortable"
|+ USB specification list
|-
! scope="row" | Spec name
! scope="row" | Issue date
! scope="row" | Maximum signaling rates: mode names
! scope="row" | Note
|-
! scope="row" | {{Nowrap|USB 0.7}}
| {{Dts|11 November 1994}}
| {{dunno}}
| rowspan="4" | Pre-release
|-
! scope="row" | {{Nowrap|USB 0.8}}
| {{Dts|30 December 1994}}
| {{dunno}}
|-
! scope="row" | {{Nowrap|USB 0.9}}
| {{Dts|13 April 1995}}
| {{Nowrap|12 Mbit/s: Full Speed (FS)}}
|-
! scope="row" | {{Nowrap|USB 0.99}}
| {{Dts|25 August 1995}}
| {{dunno}}
|-
! scope="row" | {{Nowrap|USB 1.0 FDR}}
| {{Dts|13 November 1995}}
| {{dunno}}
| Release Candidate
|-
! scope="row" | {{Nowrap|USB 1.0}}
| {{Dts|15 January 1996}}
| rowspan="2" | {{Nowrap|1.5 Mbit/s: Low Speed (LS)}} {{Nowrap|12 Mbit/s: Full Speed (FS)}}
| First official specification
|-
! scope="row" | {{Nowrap|USB 1.1}}
| {{Dts|23 September 1998}}
| Updated all chapters to fix problems identified
|-
! scope="row" | {{Nowrap|USB 2.0}}
| {{Dts|27 April 2000}}
| {{Nowrap|480 Mbit/s: High Speed (HS)}}
| Fully replaced and backward compatible with USB 1.0/1.1
|-
! scope="row" | {{Nowrap|USB 3.0}}
| {{Dts|12 November 2008}}
| {{Nowrap|5 Gbit/s: USB 3.0}}
| Fully incorporated USB 2.0 and also marketed as SuperSpeed (SS)
|-
! scope="row" | {{Nowrap|USB 3.1}}
| {{Dts|26 July 2013}}
| {{Nowrap|10 Gbit/s: USB 3.1 Gen 2}}
| Fully replaced USB 3.0 and also marketed as SuperSpeed+ (SS+)
|-
! scope="row" | {{Nowrap|USB 3.2 Revision 1.0}}
| {{Dts|22 September 2017}}
| rowspan="2" | {{Nowrap|10 Gbit/s: USB 3.2 Gen 1×2}} {{Nowrap|20 Gbit/s: USB 3.2 Gen 2×2}}
| Fully replaced USB 3.1 and requires Full-Featured USB-C Fabrics for two lane operation.
|-
! scope="row" | {{Nowrap|USB 3.2 Revision 1.1}}
| {{Dts|June 2022}}
| Incorporated errata and ECNs
|-
! scope="row" | {{Nowrap|USB4}}
| {{Dts|August 2019}}
| {{Nowrap|20 Gbit/s: USB4 Gen 3×1}} {{Nowrap|40 Gbit/s: USB4 Gen 3×2}}
| First Version, USB4 "functionally replaces" USB 3.2 while retaining the USB 2.0 bus operating in parallel.
|-
! scope="row" | {{Nowrap|USB4 Version 2.0}}
| {{Dts|October 2022}}
| {{Nowrap|80 Gbit/s: Gen 4 symmetric}} {{Nowrap|120 ⇄ 40 Gbit/s: Gen 4 asymmetric}}
| Version 2.0
|}

==== Power-related standards history====
{| class="wikitable sortable"
|+ USB power-related standards list
|-
! style="width:18em;" | Release name
! Release date
! style="width:8em;" | Max. power
|-
| USB 1.0/1.1 specification, chapter 7.2 Power Distribution and chapter 7.3 Physical Layer
| 1996-01-15/1998-09-23
| rowspan="2" | LPD: 0.5 W (5 V, 100 mA) HPD: 2.5 W (5 V, 500 mA)
|-
| USB 2.0 specification, chapter 7.2 Power Distribution and chapter 7.3 Physical Layer
| 2000-04-27
|-
| USB 3.0 specification, chapter 11 Interoperability and Power Delivery
| 2008-11-12
| rowspan="3" | LPD: 0.75 W (5 V, 150 mA) HPD: 4.5 W (5 V, 900 mA)
|-
| USB 3.1 specification, chapter 11 Interoperability and Power Delivery
| 2013-07-26
|-
| USB 3.2 Revision 1.1 specification, chapter 11 Interoperability and Power Delivery
| 2022-07
|- valign=top
| colspan="3" |
|- valign=top
| [[USB Battery Charging]] Rev. 1.0
| 2007-03-08
| rowspan=3 | 7.5 W (5 V, 1.5 A)
|-
| USB Battery Charging Rev. 1.1
| 2009-04-15
|-
| USB Battery Charging Rev. 1.2
| 2010-10-05
|- valign=top
| colspan="3" |
|- valign=top
| [[USB Power Delivery]] Rev. 1.0 (V. 1.0-1.3)
| 2012-07-05
| rowspan=3 | SPR: 100 W (20 V, 5 A)
|-
| USB Power Delivery Rev. 2.0 (V. 1.0-1.3)
| 2014-08-11
|-
| USB Power Delivery Rev. 3.0 (V. 1.0-2.0)
| 2015-12-11
|-
| USB Power Delivery Rev. 3.1 (V. 1.0-1.9)
| 2021-05-24
| rowspan=2 | EPR: 240 W (48 V, 5 A)
|-
| USB Power Delivery Rev. 3.2 (V. 1.0-1.1)
| 2023-10
|- valign=top
| colspan="3" |
|- valign=top
| [[USB Type-C]] Rev. 1.0
| 2014-08-11
| rowspan=10 | 7.5 W (5 V, 1.5 A) and/or 15 W (5 V, 3 A)
|-
| USB Type-C Rev. 1.1
| 2015-04-03
|-
| USB Type-C Rev. 1.2
| 2016-03-25
|-
| USB Type-C Rev. 1.3
| 2017-07-14
|-
| USB Type-C Rev. 1.4
| 2019-03-29
|-
| USB Type-C Rev. 2.0
| 2019-08-29
|-
| USB Type-C Rev. 2.1
| 2021-05-25
|-
|USB Type-C Rev. 2.2
|2022-10
|-
|USB Type-C Rev. 2.3
|2023-10
|-
|USB Type-C Rev. 2.4
|2024-10-28
|}

== System design ==
A USB system consists of a host with one or more downstream facing ports (DFP),<ref>{{cite web |title=Type-C CC and VCONN Signals |publisher=Microchip Technology, Inc. |url=https://microchipdeveloper.com/usb:tc-pins |access-date=August 18, 2023 |archive-date=19 August 2023 |archive-url=https://web.archive.org/web/20230819002707/https://microchipdeveloper.com/usb:tc-pins |url-status=dead }}</ref> and multiple peripherals, forming a tiered-[[star topology]]. Additional [[USB hub]]s may be included, allowing up to five tiers. A USB host may have multiple controllers, each with one or more ports. Up to 127 devices may be connected to a single host controller.<ref>{{cite web | title = Universal Serial Bus Specification Revision 2.0 | pages = 13; 30; 256 | format = [[ZIP (file format)|ZIP]] | url = http://www.usb.org/developers/docs/usb_20_101111.zip |website=USB.org | date = 11 October 2011 | access-date = 8 September 2012 | archive-url = https://web.archive.org/web/20120528075527/http://www.usb.org/developers/docs/usb_20_101111.zip | archive-date = 28 May 2012}}</ref><ref name=USB30Spec/>{{rp|at=8–29}} USB devices are linked in series through hubs. The hub built into the host controller is called the ''root hub''.

A USB device may consist of several logical sub-devices that are referred to as ''device functions''. A ''composite device'' may provide several functions, for example, a [[webcam]] (video device function) with a built-in microphone (audio device function). An alternative to this is a ''[[compound device]],'' in which the host assigns each logical device a distinct address and all logical devices connect to a built-in hub that connects to the physical USB cable.

[[File:USB pipes and endpoints (en).svg|thumb|alt=Diagram: Inside a device are several endpoints, each of which connects by a logical pipe to a host controller. Data in each pipe flows in one direction, though there is a mixture going to and from the host controller.|USB endpoints reside on the peripheral device: The channels to the host are referred to as ''pipes''.]]

USB device communication is based on ''pipes'' (logical channels). A pipe connects the host controller to a logical entity within a device, called an ''[[Communication endpoint|endpoint]]''. Because pipes correspond to endpoints, the terms are sometimes used interchangeably. Each USB device can have up to 32 endpoints (16 ''in'' and 16 ''out''), though it is rare to have so many. Endpoints are defined and numbered by the device during initialization (the period after physical connection called ''enumeration'') and so are relatively permanent, whereas pipes may be opened and closed.

There are two types of pipe: stream and message.
* A ''message'' pipe is bi-directional and is used for ''control'' transfers. Message pipes are typically used for short, simple commands to the device, and for status responses from the device, used, for example, by the bus control pipe number 0.
* A ''stream'' pipe is a uni-directional pipe connected to a uni-directional endpoint that transfers data using an ''[[isochronous]]'',<ref>{{cite web
|url=http://www.usb.org/developers/presentations/SuperSpeed_USB_DevCon_Isochronous_Froelich.pdf|title=Isochronous Protocol|date=20 May 2009|access-date=21 November 2014|author=Froelich|website=USB.org|url-status=dead|archive-url=https://web.archive.org/web/20140817061140/http://www.usb.org/developers/presentations/SuperSpeed_USB_DevCon_Isochronous_Froelich.pdf|archive-date=17 August 2014|first=Dan}}</ref> ''interrupt'', or ''bulk'' transfer:
*;Isochronous transfers: At some guaranteed data rate (for fixed-bandwidth streaming data) but with possible data loss (e.g., realtime audio or video)
*;Interrupt transfers: Devices that need guaranteed quick responses (bounded latency) such as pointing devices, [[Computer mouse|mice]], and keyboards
*;Bulk transfers: Large sporadic transfers using all remaining available bandwidth, but with no guarantees on bandwidth or latency (e.g., file transfers)

When a host starts a data transfer, it sends a TOKEN packet containing an endpoint specified with a [[tuple]] of ''(device_address, endpoint_number)''. If the transfer is from the host to the endpoint, the host sends an OUT packet (a specialization of a TOKEN packet) with the desired device address and endpoint number. If the data transfer is from the device to the host, the host sends an IN packet instead. If the destination endpoint is a uni-directional endpoint whose manufacturer's designated direction does not match the TOKEN packet (e.g. the manufacturer's designated direction is IN while the TOKEN packet is an OUT packet), the TOKEN packet is ignored. Otherwise, it is accepted and the data transaction can start. A bi-directional endpoint, on the other hand, accepts both IN and OUT packets.

[[File:Locale_RS6_USB 2 and 3.jpg|thumb|alt=Rectangular opening where the width is twice the height. The opening has a metal rim, and within the opening a flat rectangular bar runs parallel to the top side.|Two USB 3.0 Standard-A receptacles (left) and two USB 2.0 Standard-A receptacles (right) on a computer's front panel]]

Endpoints are grouped into ''interfaces'' and each interface is associated with a single device function. An exception to this is endpoint zero, which is used for device configuration and is not associated with any interface. A single device function composed of independently controlled interfaces is called a ''composite device''. A composite device only has a single device address because the host only assigns a device address to a function.

When a USB device is first connected to a USB host, the USB device enumeration process is started. The enumeration starts by sending a reset signal to the USB device. The signaling rate of the USB device is determined during the reset signaling. After reset, the USB device's information is read by the host and the device is assigned a unique 7-bit address. If the device is supported by the host, the [[device driver]]s needed for communicating with the device are loaded and the device is set to a configured state. If the USB host is restarted, the enumeration process is repeated for all connected devices.

The host controller directs traffic flow to devices, so no USB device can transfer any data on the bus without an explicit request from the host controller. In USB 2.0, the host controller [[Polling (computer science)|polls]] the bus for traffic, usually in a [[Round-robin scheduling|round-robin]] fashion. The throughput of each USB port is determined by the slower speed of either the USB port or the USB device connected to the port.

High-speed USB 2.0 hubs contain devices called transaction translators that convert between high-speed USB 2.0 buses and full and low speed buses. There may be one translator per hub or per port.

Because there are two separate controllers in each USB 3.0 host, USB 3.0 devices transmit and receive at USB 3.0 signaling rates regardless of USB 2.0 or earlier devices connected to that host. Operating signaling rates for earlier devices are set in the legacy manner.

== Device classes ==
The functionality of a USB device is defined by a class code sent to a USB host. This allows the host to load software modules for the device and to support new devices from different manufacturers.

Device classes include:<ref>{{Cite web | url = https://www.usb.org/defined-class-codes | title = USB Class Codes | date = 22 September 2018 | website = USB Implementers Forum | url-status=live | archive-url = https://web.archive.org/web/20180922111633/https://www.usb.org/defined-class-codes | archive-date = 22 September 2018}}</ref>

{| class="wikitable"
|-
! Class ([[hexadecimal|hex]])
! Usage
! Description
! Examples, or exception
|-
| 00
| Device
| Unspecified<ref>Use class information in the interface descriptors. This base class is defined to use in device descriptors to indicate that class information should be determined from the Interface Descriptors in the device.</ref>
| Device class is unspecified, interface descriptors are used to determine needed drivers
|-
| 01
| Interface
| Audio
| [[Loudspeaker|Speaker]], [[microphone]], [[sound card]], [[MIDI#USB and FireWire|MIDI]]
|-
| 02
| Both
| [[USB communications device class|Communications and CDC control]]
| [[USB adapter|Serial adapter]], [[modem]], [[Wi-Fi]] adapter, [[Ethernet]] adapter. Used together with class 0Ah ''(CDC-Data'') below
|-
| 03
| Interface
| [[USB human interface device class|Human interface device (HID)]]
| [[Keyboard (computing)|Keyboard]], [[Mouse (computing)|mouse]], joystick
|-
| 05
| Interface
| Physical interface device (PID)
| Force feedback joystick
|-
| 06
| Interface
| Media ([[Picture Transfer Protocol|PTP]]/[[Media Transfer Protocol|MTP]])
| [[Image scanner|Scanner]], [[Digital camera|Camera]]
|-
| 07
| Interface
| [[Computer printer|Printer]]
| [[Laser printer]], [[inkjet printer]], [[CNC machine]]
|-
| 08
| Interface
| [[USB mass storage]], [[USB Attached SCSI]]
| [[USB flash drive]], [[memory card reader]], [[digital audio player]], [[digital camera]], external drive
|-
| 09
| Device
| [[USB hub]]
| High speed USB hub
|-
| 0A
| Interface
| CDC-Data
| Used together with class 02h ''(Communications and CDC Control'') above
|-
| 0B
| Interface
| [[Smart card]]
| USB smart card reader
|-
| 0D
| Interface
| Content security
| Fingerprint reader
|-
| 0E
| Interface
| [[USB video device class|Video]]
| [[Webcam]]
|-
| 0F
| Interface
| Personal healthcare device class (PHDC)
| Pulse monitor (watch)
|-
| 10
| Interface
| Audio/video (AV)
| [[Webcam]], TV
|-
| 11
| Device
| Billboard
| Describes USB-C alternate modes supported by device
|-
| DC
| Both
| Diagnostic device
| USB compliance testing device
|-
| E0
| Interface
| [[Wireless]] controller
| [[Bluetooth]] adapter
|-
| EF
| Both
| Miscellaneous
| [[ActiveSync]] device
|-
| FE
| Interface
| Application-specific
| [[IrDA]] Bridge, [[RNDIS]], Test & Measurement Class (USBTMC),<ref>{{Cite web |title= Universal Serial Bus Test and Measurement Class Specification (USBTMC) Revision 1.0 |url= http://sdpha2.ucsd.edu/Lab_Equip_Manuals/USBTMC_1_00.pdf |date= 14 April 2003 |publisher= USB Implementers Forum |via= sdpha2.ucsd.edu |access-date= 10 May 2018 |archive-date= 23 December 2018 |archive-url= https://web.archive.org/web/20181223041215/http://sdpha2.ucsd.edu/Lab_Equip_Manuals/USBTMC_1_00.pdf |url-status=live}}</ref> USB DFU (Device Firmware Upgrade)<ref name="dfu-1.1">{{cite web
|url = https://www.usb.org/document-library/device-firmware-upgrade-11-new-version-31-aug-2004
|title = Universal Serial Bus Device Class Specification for Device Firmware Upgrade, Version 1.1
|date = 15 October 2004
|access-date = 8 September 2014
|publisher = USB Implementers Forum
|pages = 8–9
|url-status = live
|archive-url = https://web.archive.org/web/20141011015811/http://www.usb.org/developers/docs/devclass_docs/DFU_1.1.pdf
|archive-date = 11 October 2014
}}</ref>
|-
| FFh
| Both
| Vendor-specific
| Indicates that a device needs vendor-specific drivers
|}

=== USB mass storage / USB drive ===
{{See also|USB mass storage device class|Disk enclosure|External hard disk drive}}
[[File:Locale_RS6_SanDisk-Cruzer-USB-4GB-ThumbDrive.jpg|thumb|An early USB mass-storage device ([[USB flash drive|flash drive]]) with a USB-A type connector]]
[[File:Locale_RS6_M.2 2242 SSD connected into USB 3.0 adapter.jpg|thumb|An [[M.2]] (2242) solid-state-drive ([[SSD]]) connected into a USB 3.0 adapter connected to computer]]

The [[USB mass storage device class]] (MSC or UMS) standardizes connections to storage devices. At first intended for magnetic and optical drives, it has been extended to support [[USB flash drive|flash drives]] and [[SD card]] readers. The ability to boot a write-locked [[SD card]] with a USB adapter is particularly advantageous for maintaining the integrity and non-corruptible, pristine state of the booting medium.

Though most personal computers since early 2005 can boot from USB mass storage devices, USB is not intended as a primary bus for a computer's internal storage. However, USB has the advantage of allowing [[hot-swapping]], making it useful for mobile peripherals, including drives of various kinds.

Several manufacturers offer external portable USB [[hard disk drive]]s, or empty enclosures for disk drives. These offer performance comparable to internal drives, limited by the number and types of attached USB devices, and by the upper limit of the USB interface. Other competing standards for external drive connectivity include [[eSATA]], [[ExpressCard]], [[FireWire]] (IEEE 1394), and most recently [[Thunderbolt (interface)|Thunderbolt]].

Another use for USB mass storage devices is the portable execution of software applications (such as web browsers and VoIP clients) with no need to install them on the host computer.<ref>{{cite web | url = http://www.makeuseof.com/tag/portable-software-usb/ | title = 100 Portable Apps for your USB Stick (both for Mac and Win) | access-date = 30 October 2008 | url-status=live | archive-url = https://web.archive.org/web/20081202121455/http://www.makeuseof.com/tag/portable-software-usb/ | archive-date = 2 December 2008}}</ref><ref>{{cite web | url = http://www.VoIP-Download.com/Skype.htm#USB/ | title = Skype VoIP USB Installation Guide | access-date = 30 October 2008 | url-status=dead | archive-url = https://web.archive.org/web/20140706153501/http://www.voip-download.com/Skype.htm#USB/ | archive-date = 6 July 2014}}</ref>

=== Media Transfer Protocol ===
{{See also|Picture Transfer Protocol}}

[[Media Transfer Protocol]] (MTP) was designed by [[Microsoft]] to give higher-level access to a device's filesystem than USB mass storage, at the level of files rather than disk blocks. It also has optional [[Digital rights management|DRM]] features. MTP was designed for use with [[portable media player]]s, but it has since been adopted as the primary storage access protocol of the [[Android operating system]] from the version 4.1 Jelly Bean as well as Windows Phone 8 (Windows Phone 7 devices had used the Zune protocol—an evolution of MTP). The primary reason for this is that MTP does not require exclusive access to the storage device the way UMS does, alleviating potential problems should an Android program request the storage while it is attached to a computer. The main drawback is that MTP is not as well supported outside of Windows operating systems.

=== Human interface devices ===
{{Main|USB human interface device class}}

A USB mouse or keyboard can usually be used with older computers that have [[PS/2 port]]s with the aid of a small USB-to-PS/2 adapter. For mice and keyboards with dual-protocol support, a passive adapter that contains no [[Electronic circuit|logic circuitry]] may be used: the [[USB hardware]] in the keyboard or mouse is designed to detect whether it is connected to a USB or PS/2 port, and communicate using the appropriate protocol.{{Citation needed|date=May 2023}} Active converters that connect USB keyboards and mice (usually one of each) to PS/2 ports also exist.<ref>{{cite web |url=http://www.startech.com/Server-Management/KVM-Switches/PS-2-to-USB-Keyboard-and-Mouse-Adapter~PS22USB |title=PS/2 to USB Keyboard and Mouse Adapter |archive-url=https://web.archive.org/web/20141112214808/http://www.startech.com/Server-Management/KVM-Switches/PS-2-to-USB-Keyboard-and-Mouse-Adapter~PS22USB |website=StarTech.com |archive-date=12 November 2014 |access-date=21 May 2023}}</ref>

=== Device Firmware Upgrade mechanism ===
''Device Firmware Upgrade'' (DFU) is a generic mechanism for upgrading the [[firmware]] of USB devices with improved versions provided by their manufacturers, offering (for example) a way to deploy firmware bug fixes. During the firmware upgrade operation, USB devices change their operating mode effectively becoming a [[Programmable read-only memory|PROM]] programmer. Any class of USB device can implement this capability by following the official DFU specifications. Doing so allows use of DFU-compatible host tools to update the device.<ref name="dfu-1.1"/><ref name="dfu-1.0">{{cite web
| url = http://www.usb.org/developers/devclass_docs/usbdfu10.pdf
| archive-url = https://web.archive.org/web/20140824054756/http://www.usb.org/developers/devclass_docs/usbdfu10.pdf
| title = Universal Serial Bus Device Class Specification for Device Firmware Upgrade, Version 1.0
| date = 13 May 1999 | access-date = 8 September 2014 | archive-date = 24 August 2014
| publisher = USB Implementers Forum
| pages = 7–8
}}</ref><ref>{{cite web
| url = https://admin.fedoraproject.org/pkgdb/package/dfu-util/
| title = rpms/dfu-util: USB Device Firmware Upgrade tool
| date = 14 May 2014
| access-date = 8 September 2014
| website = fedoraproject.org
| archive-date = 8 September 2014
| archive-url = https://web.archive.org/web/20140908112041/https://admin.fedoraproject.org/pkgdb/package/dfu-util/
| url-status = live
}}</ref>

DFU is sometimes used as a flash memory programming protocol in microcontrollers with built-in USB bootloader functionality.
<ref>{{cite web
| url = https://www.st.com/resource/en/application_note/cd00264379-usb-dfu-protocol-used-in-the-stm32-bootloader-stmicroelectronics.pdf
| title = AN3156: USB DFU protocol used in the STM32 bootloader
| date = 7 February 2023
| access-date = 28 January 2024
| website = st.com
|archive-url=https://web.archive.org/web/20260104205331/https://www.st.com/resource/en/application_note/cd00264379-usb-dfu-protocol-used-in-the-stm32-bootloader-stmicroelectronics.pdf |archive-date=2026-01-04}}</ref>

Examples of devices can using DFU include [[iPod]] and [[iPhone]].<ref> {{Cite web |title=If you can't update or restore your iPhone or iPod touch |url=https://support.apple.com/en-us/118106 |access-date=2026-04-01 |website=Apple Support |language=en}}</ref>

=== Audio streaming ===
The USB Device Working Group has laid out specifications for audio streaming, and specific standards have been developed and implemented for audio class uses, such as microphones, speakers, headsets, telephones, musical instruments, etc. The working group has published four versions of audio device specifications:<ref>{{Cite press release |date=27 September 2016 |title=USB-IF Announces USB Audio Device Class 3.0 Specification |location=Houston, Texas & Beaverton, Oregon |url=https://www.businesswire.com/news/home/20160927006252/en/USB-IF-Announces-USB-Audio-Device-Class-3.0 |website=Business Wire |access-date=4 May 2018 |archive-date=4 May 2018 |archive-url=https://web.archive.org/web/20180504155618/https://www.businesswire.com/news/home/20160927006252/en/USB-IF-Announces-USB-Audio-Device-Class-3.0 |url-status=live }}</ref><ref>{{Cite web |url=http://www.usb.org/developers/docs/devclass_docs/ |title=USB Device Class Specifications |website=www.usb.org |access-date=4 May 2018 |archive-date=13 August 2014 |archive-url=https://web.archive.org/web/20140813051139/http://www.usb.org/developers/docs/devclass_docs/ |url-status=live }}</ref><ref>{{Cite web |title=USB Audio Devices Release 4.0 and Adopters Agreement {{!}} USB-IF |url=https://www.usb.org/document-library/usb-audio-devices-release-40-and-adopters-agreement |access-date=2025-05-20 |website=www.usb.org}}</ref> USB Audio 1.0, 2.0, 3.0 and 4.0, referred to as "USB Audio Class" (UAC)<ref name="xmos2015"/> or "Audio Device Class" (ADC).<ref>{{Cite web |url=https://docs.microsoft.com/en-us/windows-hardware/drivers/audio/usb-2-0-audio-drivers |title=USB Audio 2.0 Drivers |website=Microsoft Hardware Dev Center |access-date=4 May 2018 |quote=ADC-2 refers to the USB Device Class Definition for Audio Devices, Release 2.0. |archive-date=4 May 2018 |archive-url=https://web.archive.org/web/20180504155514/https://docs.microsoft.com/en-us/windows-hardware/drivers/audio/usb-2-0-audio-drivers |url-status=live }}</ref>

UAC 3.0 primarily introduces improvements for portable devices, such as reduced power usage by bursting the data and staying in low power mode more often, and power domains for different components of the device, allowing them to be shut down when not in use.<ref>{{Cite web|url=https://www.synopsys.com/designware-ip/technical-bulletin/usb-audio-dwtb-q117.html|title=New USB Audio Class for USB Type-C Digital Headsets|website=Synopsys.com|access-date=7 May 2018|archive-date=7 May 2018|archive-url=https://web.archive.org/web/20180507221645/https://www.synopsys.com/designware-ip/technical-bulletin/usb-audio-dwtb-q117.html|url-status=live}}</ref>

UAC 2.0 introduced support for High Speed USB (in addition to Full Speed), allowing greater bandwidth for multi-channel interfaces, higher sample rates,<ref name=":2">{{Cite web |url=http://thewelltemperedcomputer.com/KB/USB.html |title=USB |website=The Well-Tempered Computer |last=Kars |first=Vincent |date=May 2011 |access-date=7 May 2018 |quote=All operating systems (Win, OSX, and Linux) support USB Audio Class 1 natively. This means you don't need to install drivers, it is plug&play. |archive-date=7 May 2018 |archive-url=https://web.archive.org/web/20180507153825/http://thewelltemperedcomputer.com/KB/USB.html |url-status=live }}</ref> lower inherent latency,<ref>{{Cite web |url=https://www.xmos.ai/file/fundamentals-of-usb-audio?version=latest |title=Fundamentals of USB Audio |publisher=XMOS Ltd. |website=www.xmos.com |format=PDF |date=2015 |access-date=10 December 2020 |quote=Note that Full Speed USB has a much higher intrinsic latency of 2ms }}{{Dead link|date=January 2026 |bot=InternetArchiveBot }}</ref><ref name="xmos2015"/> and 8× improvement in timing resolution in synchronous and adaptive modes.<ref name="xmos2015"/> UAC2 also introduced the concept of clock domains, which provides information to the host about which input and output terminals derive their clocks from the same source, as well as improved support for audio encodings like [[Direct Stream Digital|DSD]], audio effects, channel clustering, user controls, and device descriptions.<ref name="xmos2015"/><ref name=":4"/>

UAC 1.0 devices are still common, however, due to their cross-platform driverless compatibility,<ref name=":2"/> and also partly due to [[Microsoft Windows|Microsoft]]'s failure to implement UAC 2.0 for over a decade after its publication, having finally added support to [[Windows 10]] through the Creators Update on 20 March 2017.<ref>{{Cite web |url=https://blogs.windows.com/windowsexperience/2016/09/21/announcing-windows-10-insider-preview-build-14931-for-pc/ |title=Announcing Windows 10 Insider Preview Build 14931 for PC |website=Windows Experience Blog |date=21 September 2016 |access-date=7 May 2018 |quote=We now have native support for USB Audio 2.0 devices with an inbox class driver! This is an early version of the driver that does not have all features enabled |archive-date=23 September 2016 |archive-url=https://web.archive.org/web/20160923032703/https://blogs.windows.com/windowsexperience/2016/09/21/announcing-windows-10-insider-preview-build-14931-for-pc/ |url-status=live }}</ref><ref>{{Cite web |url=http://amplioaudio.blogspot.com/2017/09/usb-audio-class-20-support-in-windows.html |title=Ampliozone: USB Audio Class 2.0 Support in Windows 10, FINALLY!!!! |last=Plummer |first=Gregg |date=20 September 2017 |website=Ampliozone |access-date=7 May 2018 |archive-date=7 May 2018 |archive-url=https://web.archive.org/web/20180507154036/http://amplioaudio.blogspot.com/2017/09/usb-audio-class-20-support-in-windows.html |url-status=live }}</ref><ref name=":4">{{Cite web|url=https://www.computeraudiophile.com/ca/bits-and-bytes/this-just-in-microsoft-launches-native-class-2-usb-audio-support-wait-what-r647/|title=This Just In: Microsoft Launches Native Class 2 USB Audio Support. Wait, What?|website=Computer Audiophile|date=2 May 2017 |access-date=7 May 2018|quote=Class 2 support enables much higher sample rates such as PCM 24 bit / 384 kHz and DSD (DoP) up through DSD256.|archive-date=2 September 2018|archive-url=https://web.archive.org/web/20180902023557/https://www.computeraudiophile.com/ca/bits-and-bytes/this-just-in-microsoft-launches-native-class-2-usb-audio-support-wait-what-r647/|url-status=live}}</ref> UAC 2.0 is also supported by [[macOS]], [[iOS]], and [[Linux]],<ref name="xmos2015"/> however [[Android (operating system)|Android]] only implements a subset of the UAC 1.0 specification.<ref name=":5">{{Cite web |url=https://source.android.com/docs/core/audio/usb#hostAudio |title=USB Digital Audio |website=Android Open Source Project |access-date=16 February 2023 |quote=Synchronous sub-mode is not commonly used with audio because both host and peripheral are at the mercy of the USB clock. }}</ref>

USB provides three isochronous (fixed-bandwidth) synchronization types,<ref>{{cite web|url=http://www.atmel.com/Images/doc32139.pdf|title=32-bit Atmel Microcontroller Application Note|date=2011|publisher=Atmel Corporation|access-date=13 April 2016|url-status=live|archive-url=https://web.archive.org/web/20160506204128/http://www.atmel.com/Images/doc32139.pdf|archive-date=6 May 2016}}</ref> all of which are used by audio devices:<ref>{{Cite web|url=http://www.ti.com/lit/ds/symlink/pcm2906c.pdf|title=PCM2906C datasheet|date=November 2011|website=Texas Instruments|quote=The PCM2906C employs SpAct architecture, TI's unique system that recovers the audio clock from USB packet data.|access-date=4 May 2018|archive-date=4 May 2018|archive-url=https://web.archive.org/web/20180504225235/http://www.ti.com/lit/ds/symlink/pcm2906c.pdf|url-status=live}}</ref>

* Asynchronous — The ADC or DAC are not synced to the host computer's clock at all, operating off a free-running clock local to the device.
* Synchronous — The device's clock is synced to the USB start-of-frame (SOF) or Bus Interval signals. For instance, this can require syncing an 11.2896 MHz clock to a 1 kHz SOF signal, a large frequency multiplication.<ref>{{Cite web|url=http://www.cypress.com/file/102921/download|title=Designing Modern USB Audio Systems|last=Castor-Perry|first=Kendall|date=October 2010|website=Cypress Semiconductor|access-date=4 May 2018|archive-date=5 May 2018|archive-url=https://web.archive.org/web/20180505172950/http://www.cypress.com/file/102921/download|url-status=live}}</ref><ref name=":1">{{Cite web|url=http://www.cypress.com/file/122521/download|title=Programmable Clock Generation and Synchronization for USB Audio Systems|last=Castor-Perry|first=Kendall|date=2011|website=Cypress Semiconductor|quote=Early USB replay interfaces used synchronous mode but acquired a reputation for poor quality of the recovered clock (and resultant poor replay quality). This was primarily due to deficiencies of clocking implementation rather than inherent shortcomings of the approach.|access-date=4 May 2018|archive-date=4 May 2018|archive-url=https://web.archive.org/web/20180504181023/http://www.cypress.com/file/122521/download|url-status=live}}</ref>
* Adaptive — The device's clock is synced to the amount of data sent per frame by the host<ref>{{Cite web|url=http://www.thewelltemperedcomputer.com/Lib/Hitoshi%20Kondoh%20story.pdf|title=The D/A diaries: A personal memoir of engineering heartache and triumph|last=Kondoh|first=Hitoshi|date=20 February 2002|quote=The fact that there is no clock line within the USB cable leads to a thinner cable, which is an advantage. But, no matter how good the crystal oscillators are at the send and receive ends, there will always be some difference between the two...|access-date=4 May 2018|archive-date=12 December 2019|archive-url=https://web.archive.org/web/20191212230749/http://www.thewelltemperedcomputer.com/Lib/Hitoshi%20Kondoh%20story.pdf|url-status=live}}</ref>

While the USB spec originally described asynchronous mode being used in "low cost speakers" and adaptive mode in "high-end digital speakers",<ref>{{Cite web |url=http://www.usb.org/developers/docs/usb20_docs/ |title=USB 2.0 Documents |website=www.usb.org |access-date=7 May 2018 |archive-date=3 December 2017 |archive-url=https://web.archive.org/web/20171203144114/http://www.usb.org/developers/docs/usb20_docs/ |url-status=live }}</ref> the opposite perception exists in the [[hi-fi]] world, where asynchronous mode is advertised as a feature, and adaptive/synchronous modes have a bad reputation.<ref>{{Cite web |url=https://www.cambridgeaudio.com/usa/en/blog/our-guide-usb-audio-why-should-i-use-it |title=Our Guide to USB Audio – Why Should I Use it? |website=Cambridge Audio |date=9 May 2016 |access-date=7 May 2018 |quote=Synchronous USB DAC is the lowest quality of the three ... Adaptive ... means that there is no continuous, accurate master clock in the DAC, which causes jitter in the audio stream. ... Asynchronous – this is the most complex to implement but it is a huge improvement on the other types. |archive-date=7 May 2018 |archive-url=https://web.archive.org/web/20180507153701/https://www.cambridgeaudio.com/usa/en/blog/our-guide-usb-audio-why-should-i-use-it |url-status=live }}</ref><ref>{{Cite web |url=http://thewelltemperedcomputer.com/Intro/SQ/USB_USB.htm |title=USB versus USB |website=The Well-Tempered Computer |last=Kars |first=Vincent |date=July 2012 |access-date=7 May 2018 |quote=Synchronous is not used in a quality DAC as it is very jittery. ... asynchronous is the better of these modes. |archive-date=22 April 2018 |archive-url=https://web.archive.org/web/20180422204100/http://thewelltemperedcomputer.com/Intro/SQ/USB_USB.htm |url-status=live }}</ref><ref name=":5"/> In reality, all types can be high-quality or low-quality, depending on the quality of their engineering and the application.<ref name=":1"/><ref name="xmos2015"/><ref>{{Cite web |url=https://www.head-fi.org/threads/low-jitter-usb-dan-lavry-michael-goodman-adaptive-asynchronous.493152/#post-6661517 |title=Low-Jitter USB: Dan Lavry, Michael Goodman, Adaptive, Asynchronous |website=Head-Fi |access-date=7 May 2018 |quote=Some manufacturers may lead you to believe that Asynchronous USB transfers are superior to Adaptive USB transfers and that therefore you must believe in the asynchronous solution. This no more true than saying that you "must" hold the fork in your left hand. In fact, if you know what you are doing, you will feed yourself with either hand. The issue is really about good engineering practices. |archive-date=7 May 2018 |archive-url=https://web.archive.org/web/20180507153738/https://www.head-fi.org/threads/low-jitter-usb-dan-lavry-michael-goodman-adaptive-asynchronous.493152/#post-6661517 |url-status=live }}</ref> Asynchronous has the benefit of being untied from the computer's clock, but the disadvantage of requiring [[sample rate conversion]] when combining multiple sources.

== Connectors ==
{{Main|USB hardware#Connectors}}
[[File:USB A, B, C (1.1-3.0) connectors.svg|thumb|upright=1.5|Comparison of most ''legacy'' USB and current USB Type-C connectors]]
The connectors the USB committee specifies support a number of USB's underlying goals, and reflect lessons learned from the many connectors the computer industry has used. The female connector mounted on the host or device is called the ''receptacle'', and the male connector attached to the cable is called the ''plug''.<ref name=USB30Spec/>{{rp|pages=2-5–2-6}} The official USB specification documents also periodically define the term ''male'' to represent the plug, and ''female'' to represent the receptacle.<ref>{{cite web |title=USB 2.0 Specification Engineering Change Notice (ECN) #1: Mini-B connector | website = USB Implementers Forum |url=http://www.usb.org/developers/docs/ecn1.pdf |date=20 October 2000 |url-status=live |archive-url=https://web.archive.org/web/20150412121600/http://www.usb.org/developers/docs/ecn1.pdf |archive-date=12 April 2015 |access-date=29 December 2014}}</ref>

The design is intended to make it difficult to insert a USB plug into its receptacle incorrectly. The USB specification requires that the cable plug and receptacle be marked so the user can recognize the proper orientation.<ref name=USB30Spec/> The USB-C plug however is reversible. USB cables and small USB devices are held in place by the gripping force from the receptacle, with no screws, clips, or thumb-turns as some connectors use.

The distinction of ''A'' and ''B'' connectors was to enforce the directionality inherent in USB: The single ''host'' has Type‑A receptacles and each ''peripheral device'' has a single Type‑B receptacle. A ''hub'' provides multiple ''downstream''-facing Type‑A receptacles and connects to the host through its single Type‑B receptacle (or a captive cable with a Type‑A plug). A hub may connect to the host either directly or through one or more additional hubs. Prior to Type‑C, [[USB On-The-Go]] allowed a device such as a smartphone to take either the ''host'' or the ''peripheral device'' role, with a single Type‑AB receptacle (Micro‑AB, superseded in 2014, or Mini-AB, deprecated 2007<ref name="Deprecation of Mini-A and Mini-AB">{{cite press release |publisher=USB Implementers Forum |title=Deprecation of the Mini-A and Mini-AB Connectors |date=May 27, 2007 |access-date=January 13, 2009 |url=http://www.usb.org/developers/Deprecation_Announcement_052507.pdf |url-status=dead |archive-url=https://web.archive.org/web/20090306145248/http://www.usb.org/developers/Deprecation_Announcement_052507.pdf |archive-date=March 6, 2009}}</ref>) that accepted both Type‑A and Type‑B plugs.

USB connector types multiplied as the specification progressed. The original USB specification detailed Standard‑A and Standard‑B plugs and receptacles. These were originally referred to as simply ''Type‑A'' and ''Type‑B''; they were renamed ''Standard'' out of necessity to distinguish from Mini and later Micro connectors. The data contacts in the Standard plugs are recessed compared to the power and ground contacts so that devices are safely electrically connected before the more delicate data communications circuitry is connected, preventing damage. Some devices operate in different modes depending on whether the data connection is made. Simple power sources do not include data connections, instead shorting the data contacts together, but allow any capable USB device to charge or operate through a standard USB cable. Charging cables provide power connections but not data, though the standard requires at least a USB 2.0 data connection capability. In a non-standard charge-only cable, the data wires are shorted at the device end; otherwise, the device may reject the charger as unsuitable.

{{Clear}}

== Cabling ==
{{Main|USB hardware#Cabling}}
[[File:Locale_RS6_Cables in Hong Kong.JPG|thumb|A variety of USB cables for sale in [[Hong Kong]] ]]

The USB 1.1 standard specifies that a standard cable can have a maximum length of {{convert|5|m|ftin|sp=us}} with devices operating at full speed (12 Mbit/s), and a maximum length of {{convert|3|m|ftin|sp=us}} with devices operating at low speed (1.5 Mbit/s).<ref>{{cite web |url=http://www.cablesplususa.com/pdf/USB_Cable_Length_Limitations.pdf |title=USB Cable Length Limitations |website=CablesPlusUSA.com |date=3 November 2010 |access-date=2 February 2014 |archive-url=https://web.archive.org/web/20141011015850/http://www.cablesplususa.com/pdf/USB_Cable_Length_Limitations.pdf |archive-date=11 October 2014}}</ref><ref>{{cite web |url=https://www.techwalla.com/articles/what-is-the-maximum-length-of-a-usb-cable |title=What Is the Maximum Length of a USB Cable? |website=Techwalla.com |access-date=18 November 2017 |url-status=live |archive-url=https://web.archive.org/web/20171201043247/https://www.techwalla.com/articles/what-is-the-maximum-length-of-a-usb-cable |archive-date=1 December 2017}}</ref><ref name="faq"/>

USB 2.0 provides for a maximum cable length of {{convert|5|m|ftin|sp=us}} for devices running at high speed (480 Mbit/s).<ref name="faq">{{Cite web | url = http://www.usb.org/developers/usbfaq/#cab1 | title = Cables and Long-Haul Solutions | work = USB 2.0 Frequently Asked Questions | publisher = USB Implementers Forum | access-date = 28 April 2019 | url-status=dead | archive-url = https://web.archive.org/web/20110118225750/http://www.usb.org/developers/usbfaq/#cab1 | archive-date = 18 January 2011}}</ref>

The USB 3.0 standard does not directly specify a maximum cable length, requiring only that all cables meet an electrical specification: for copper cabling with [[AWG]] 26 wires the maximum practical length is {{convert|3|m|ftin|sp=us}}.<ref>{{cite web |title=USB 3.0 Developers FAQ |url=http://janaxelson.com/usb3faq.htm#ca_maximum |access-date=20 October 2016 |last=Axelson |first=Jan |url-status=live |archive-url=https://web.archive.org/web/20161220073858/http://www.janaxelson.com/usb3faq.htm#ca_maximum |archive-date=20 December 2016 }}</ref>

=== USB bridge "cables" ===
Two computers (''hosts'') can easily be connected through a USB‑C cable, but before Type‑C hosts could not be connected to each other with common USB cables. USB bridge "cables", or data transfer cables, can be found within the market, offering direct PC to PC connections. A bridge "cable" is actually an electronic device that appears as a USB ''peripheral device'' to each of the connected ''hosts'', allowing peer-to-peer communication between the computers. Such USB bridge cables are used to transfer files between two computers via their USB ports.

Popularized by Microsoft as [[Windows Easy Transfer]], the Microsoft utility used a special USB bridge cable to transfer personal files and settings from a computer running an earlier version of Windows to a computer running a newer version. In the context of the use of ''Windows Easy Transfer'' software, the bridge cable can sometimes be referenced as ''Easy Transfer cable''.

Many USB bridge / data transfer cables are still USB 2.0, but there are also a number of USB 3.0 transfer cables. Despite USB 3.0 being ten times as fast as USB 2.0, USB 3.0 transfer cables are only two to three times as fast given their design.{{clarify|reason="given their design" suggests there are reasons for this, what are they?|date=October 2022}}

The USB 3.0 specification introduced an A-to-A cross-over cable without power for connecting two PCs. These are not meant for data transfer but are aimed at diagnostic uses.

==== Dual-role USB connections ====
USB bridge cables have become less important with USB dual-role-device capabilities introduced with the USB 3.1 specification. Under the most recent specifications, USB supports most scenarios connecting systems directly with a Type-C cable. For the capability to work, however, connected systems must support role-switching. Dual-role capability requires there be ''two'' controllers within the system, as well as a ''role controller''. While this can be expected in a mobile platform such as a tablet or a phone, desktop PCs and laptops often do not support dual roles.<ref>{{cite web |url=https://superuser.com/questions/1080002/usb-3-1-type-c-host-to-host|title=USB 3.1 – Type-C Host to Host|website=superuser.com|access-date=21 July 2021|archive-date=14 October 2021|archive-url=https://web.archive.org/web/20211014022330/https://superuser.com/questions/1080002/usb-3-1-type-c-host-to-host|url-status=live}}</ref>

== Power ==
{{Main|USB hardware#Power}}

USB host and hub recepticles supply power at a nominal 5 V DC via the V_BUS pin to upstreaming USB devices.

=== Low-power and high-power devices ===
This section describes the power distribution model of USB that existed before [[USB hardware#USB Power Delivery|Power-Delivery]] (USB-PD). On devices that do not use BC or PD, USB provides up to 4.5 W through Type-A and Type-B connectors, and up to 15 W through USB-C. All pre-PD USB power is provided at 5 V.

For a host providing power to devices, USB has a concept of the ''unit load''. Any device may draw power of one unit, and devices may request more power in these discrete steps. It is not required that the host provide requested power, and a device may not draw more power than negotiated.

''Low-power'' devices can draw no more than one unit. All devices must act as low-power devices when starting out as unconfigured. For USB devices up to USB 2.0 a unit load is 100 mA (or 500 mW), while USB 3.0 defines a unit load as 150 mA (750 mW). Full-featured USB-C can support low-power devices with a unit load of 250 mA (or 1250 mW).

''High-power'' devices, e.g. typical 2.5-inch hard disk drives, can draw more than one unit. USB up to 2.0 allows a host or hub to provide up to 2.5 W to each device, in five discrete steps of 100 mA, and SuperSpeed devices (USB 3.x) allows a host or a hub to provide up to 4.5 W in six steps of 150 mA.
USB-C allows for dual-lane operation of USB 3.x with larger unit load (250 mA; up to 7.5 W).<ref>{{Cite web |title=USB 3.2 Revision 1.1|url=https://usb.org/document-library/usb-32-revision-11-june-2022|access-date=2024-12-31|website=usb.org|publisher=USB Implementers Forum|at=p. 470, section 11.4.5 Vbus Electrical Characteristics|date=June 2022}}</ref> USB-C also allows for Type-C Current as a replacement for USB BC, signaling power availability in a simple way, without needing any data connection.<ref>{{Cite web |title=USB Type-C® Cable and Connector Specification Release 2.4 {{!}} USB-IF |url=https://usb.org/document-library/usb-type-cr-cable-and-connector-specification-release-24 |access-date=2024-12-31 |website=usb.org |publisher= USB Implementers Forum |at=p41, sec. 2.4 Vbus}}</ref>

{| class="wikitable sortable" style="margin:0 0 1em 1em;"
|+ USB power standards
|-
! Specification
! max current
! Voltage
! max power
|-
| Low-power device up to USB 2.0
| {{right|100 mA}} || {{right|5 V}}{{Efn |name="Vdrop" |The V{{sub |BUS}} supply from a low-powered hub port may drop to 4.40 V.}} || {{right|0.50 W}}
|-
| Low-power SuperSpeed / USB 3.x device
| {{right|150 mA}} || {{right|5 V}}{{Efn |name="Vdrop"}} || {{right|0.75 W}}
|-
| High-power device up to USB 2.0
| {{right|500 mA}}{{Efn|Up to five unit loads; with non-SuperSpeed devices, one unit load is 100 mA.}} || {{right|5 V}} || {{right|2.5 W}}
|-
| High-power SuperSpeed / USB 3.x single-lane device
| {{right|900 mA}}{{Efn|Up to six unit loads; with SuperSpeed devices, one unit load is 150 mA.}} || {{right|5 V}} || {{right|4.5 W}}
|-
| High-power SuperSpeed / USB 3.x dual-lane device{{Efn|name="usbcOnly"|for USB-C only}}
| {{right|1.5 A}}{{Efn|name="Vml"|Up to six unit loads; with multi-lane devices, one unit load is 250 mA.}} || {{right|5 V}} || {{right|7.5 W}}
|-
| Battery Charging (BC)
| {{right|1.5 A}} || {{right|5 V}} || {{right|7.5 W}}
|-
| Type-C
| {{right|1.5 A, 3 A}} || {{right|5 V}} || {{right|7.5 W, 15 W}}
|-
| [[USB Power Delivery|Power Delivery]] {{abbr|SPR|Standard Power Range}}{{Efn|name="usbcOnly"}}
| {{right|5 A}}{{efn|name="req_5A_cable"|>3 A (>60 W) operation requires an electronically marked cable rated at 5 A.}} || {{right|up to 20 V}} || {{right|100 W}}
|-
| Power Delivery {{abbr|EPR|Extended Power Range}}{{Efn|name="usbcOnly"}}
| {{right|5 A}}{{efn|name="req_5A_cable"}} || {{right|up to 48 V}}{{efn|name="req_EPR_cable"|>20 V (>100 W) operation requires an electronically marked Extended Power Range (EPR) cable.}} || {{right|240 W}}
|-
| colspan=4 | {{notelist}}
|}

To recognize Battery Charging mode, a dedicated charging port places a resistance not exceeding 200 Ω across the D+ and D− terminals. Shorted or near-shorted data lanes with less than 200 Ω of resistance across the D+ and D− terminals signify a dedicated charging port (DCP) with indefinite charging rates.<ref name="USBBC1.2">{{cite web| url = http://www.usb.org/developers/docs/devclass_docs/BCv1.2_070312.zip | title = Battery Charging Specification, Revision 1.2 | date = 7 December 2010 | access-date = 29 March 2016 | publisher = USB Implementers Forum | url-status=dead | archive-url = https://web.archive.org/web/20160328102350/http://www.usb.org/developers/docs/devclass_docs/BCv1.2_070312.zip | archive-date = 28 March 2016 |page=45}}</ref><ref>{{cite web |title=OVERVIEW OF USB BATTERY CHARGING REVISION 1.2 AND THE IMPORTANT ROLE OF ADAPTER EMULATORS |url=https://pdfserv.maximintegrated.com/en/an/TUT5801.pdf |publisher=maxim integrated |page=3 |date=2014 |access-date=12 August 2021 |archive-date=4 July 2021 |archive-url=https://web.archive.org/web/20210704221311/https://pdfserv.maximintegrated.com/en/an/TUT5801.pdf |url-status=live}}</ref>

In addition to standard USB, there is a proprietary high-powered system known as [[PoweredUSB]], developed in the 1990s, and mainly used in point-of-sale terminals such as cash registers.

== Signaling ==
{{Main|USB communications#Signaling (USB PHY)}}

USB signals are transmitted using [[differential signaling]] on [[twisted-pair]] data wires with {{nowrap|90 [[ohm|Ω]] ± 15%}} [[characteristic impedance]].<ref>{{cite web |title=USB in a NutShell — Chapter 2: Hardware |url=http://www.beyondlogic.org/usbnutshell/usb2.htm |publisher=Beyond Logic.org |access-date=25 August 2007 |url-status=live |archive-url=https://web.archive.org/web/20070820221226/http://www.beyondlogic.org/usbnutshell/usb2.htm |archive-date=20 August 2007 }}</ref> USB 2.0 and earlier specifications define a single pair in [[half-duplex]] (HDx). USB 3.0 and later specifications define one dedicated pair for USB 2.0 compatibility and two or four pairs for data transfer: two data wire pairs realising full-duplex (FDx) for single lane (''×1'') variants require at least SuperSpeed (SS) connectors; four pairs realising full-duplex for two lane (''×2'') variants require USB-C connectors.

USB4 Gen 4 requires the use of all four pairs but allow for asymmetrical pairs configuration.<ref>{{Cite web |title=USB4 Specification v2.0 {{!}} USB-IF |url=https://www.usb.org/document-library/usb4r-specification-v20 |access-date=2023-07-22 |website=www.usb.org}}</ref> In this case one data wire pair is used for the upstream data and the other three for the downstream data or vice-versa. USB4 Gen 4 use [[pulse-amplitude modulation]] on three levels, providing a [[ternary numeral system|trit]] of information every [[baud]] transmitted, the transmission frequency of 12.8 GHz translate to a transmission rate of 25.6 GBd<ref>{{Cite web |title=USB4 Version 2.0 from Simulation to Tx, Rx, and Interconnect Test {{!}} Signal Integrity Journal |url=https://www.signalintegrityjournal.com/articles/3114-usb4-version-20-from-simulation-to-tx-rx-and-interconnect-test |access-date=2023-07-22 |website=www.signalintegrityjournal.com |language=en}}</ref> and the 11-bit–to–7-trit translation provides a theoretical maximum transmission speed just over 40.2 Gbit/s.<ref>{{Cite web |title=Welcome to the 80Gpbs Ultra-High Speed Era of USB4 {{!}} GraniteRiverLabs |url=https://www.graniteriverlabs.com/en-us/technical-blog/usb4-80-cio80 |access-date=2023-07-22 |website=www.graniteriverlabs.com }}</ref>

{{mw-datatable}}
{| class="wikitable sortable mw-datatable" style="text-align:center;"
|+ USB Data operation modes
|-
! colspan="2" |Operation mode name
! rowspan="2" |Introduced in
! rowspan="2" |Lanes
! rowspan="2" |[[Line code|Encoding]]
! rowspan="2" | # data wires
! rowspan="2" data-sort-type=number | Nominal signaling rate
! rowspan="2" |Original label
! colspan="2" |[[USB-IF]] current<ref name="USB data performance language usage 2024-01"/>
|-
! current
! class=unsortable | old
! marketing name
! class=unsortable | logo
|-
|Low-Speed
| rowspan="3" {{n/a}}
| rowspan="2" |USB 1.0
| rowspan="3" |1 [[half-duplex|HDx]]
| rowspan="3" |[[NRZI]]
| rowspan="3" | 2
| data-sort-value=0.001 | 1.5 Mbit/s half-duplex
| Low-Speed USB (LS)
| rowspan="2" |Basic-Speed USB
| rowspan="2" |[[File:Certified USB.svg|50x50px]]
|-
|Full-Speed
| data-sort-value=0.012 | 12 Mbit/s half-duplex
|Full-Speed USB (FS)
|-
|High-Speed
|USB 2.0
| data-sort-value=0.480 | 480 Mbit/s half-duplex
|colspan=2|Hi-Speed USB (HS)
| [[File:Certified Hi-Speed USB.svg|50px]]
|-
|USB 3.2 Gen 1{{Abbr|×1|single-lane}}
|USB 3.0, USB 3.1 Gen 1
|[[USB 3.0]]
| rowspan="2" |1 [[Full duplex|FDx]] (+ 1 HDx){{efn|name="HDx"}}
|[[8b/10b]]
| rowspan="2" |6
|5 <abbr>Gbit/s</abbr> symmetric
|SuperSpeed USB (SS)
|USB 5Gbps
|[[File:USB 5Gbps logo.svg|class=skin-invert-image|50px]]
|-
|USB 3.2 Gen 2{{Abbr|×1|single-lane}}
|USB 3.1 Gen 2
|[[USB 3.1]]
|[[128b/132b]]
|10 <abbr>Gbit/s</abbr> symmetric
|SuperSpeed+ (SS+)
|rowspan="2" |USB 10Gbps
|rowspan="2" |[[File:USB 10Gbps logo.svg|class=skin-invert-image|50px]]
|-
|USB 3.2 Gen 1{{Abbr|×2|two-lane}}
|rowspan="9" {{n/a}}
|rowspan="2" |[[USB 3.2]]
| rowspan="2" | 2 FDx (+ 1 HDx){{efn|name="HDx"}}
|8b/10b
| rowspan="2" | 10
|10 <abbr>Gbit/s</abbr> symmetric
| {{n/a}}
|-
|USB 3.2 Gen 2{{Abbr|×2|two-lane}}
|128b/132b
|20 <abbr>Gbit/s</abbr> symmetric
|SuperSpeed USB 20Gbps
|USB 20Gbps
|[[File:USB 20Gbps logo.svg|class=skin-invert-image|50px]]
|-
|USB4 Gen 2{{Abbr|×1|single-lane}}
|rowspan="4" |[[USB4]]
|1 FDx (+ 1 HDx){{efn|name="HDx"}}
| rowspan="2" |64b/66b{{efn|name="rs-fec"}}
|6 (used of 10)
|10 <abbr>Gbit/s</abbr> symmetric
| colspan=2| USB 10Gbps
|[[File:USB 10Gbps logo.svg|class=skin-invert-image|50px]]
|-
|USB4 Gen 2{{Abbr|×2|two-lane}}
|2 FDx (+ 1 HDx){{efn|name="HDx"}}
|10
|20 <abbr>Gbit/s</abbr> symmetric
|colspan="2" rowspan="2" |USB 20Gbps
|rowspan="2" |[[File:USB 20Gbps logo.svg|class=skin-invert-image|50px]]
|-
|USB4 Gen 3{{Abbr|×1|single-lane}}
|1 FDx (+ 1 HDx){{efn|name="HDx"}}
| rowspan="2" |128b/132b{{efn|name="rs-fec"}}
|6 (used of 10)
|20 <abbr>Gbit/s</abbr> symmetric
|-
|USB4 Gen 3{{Abbr|×2|two-lane}}
|2 FDx (+ 1 HDx){{efn|name="HDx"}}
|10
|40 <abbr>Gbit/s</abbr> symmetric
| colspan=2 | USB 40Gbps
|[[File:USB 40Gbps logo 01.svg|class=skin-invert-image|50px]]
|-
| rowspan="3" |USB4 Gen 4{{Abbr|×2|two-lane}}
| rowspan="3" |[[USB4 2.0]]
|2 FDx (+ 1 HDx){{efn|name="HDx"}}
| rowspan="3" |[[Pulse-amplitude modulation|PAM-3]] 11b/7[[Ternary numeral system|t]]
| rowspan="3" |10
|80 Gbit/s symmetric
| colspan=2 | USB 80Gbps
|[[File:USB 80Gbps logo.svg|class=skin-invert-image|50px]]
|-
| rowspan="2" | asymmetric (+ 1 HDx){{efn|name="HDx"}}
|40 Gbit/s up 120 Gbit/s down
| colspan="3" rowspan="2" {{N/A}}
|-
|120 Gbit/s up 40 Gbit/s down
|}

{{notelist|refs=
{{efn|name="rs-fec"| USB4 can use optional [[Reed–Solomon]] [[Error correction code#Forward error correction|forward error correction]] (RS FEC). In this mode, 12 × 16 B (128 bit) symbols are assembled together with 2 B (12 bit + 4 bit reserved) synchronization bits indicating the respective symbol types and 4 B of RS FEC to allow to correct up to 1 B of errors anywhere in the total 198 B block.}}

{{efn|name="HDx"|USB 2.0 implementation}}
}}

* '''Low-speed (LS)''' and '''Full-speed (FS)''' modes use a single data wire pair, labeled D+ and D−, in [[half-duplex]]. Transmitted signal levels are {{nowrap|0.0–0.3 V}} for logical low, and {{nowrap|2.8–3.6 V}} for logical high level. The signal lines are not [[electrical termination|terminated]].
* '''High-speed (HS)''' uses the same wire pair, but with different electrical conventions. Lower signal voltages of {{nowrap|−10 to 10 mV}} for low and {{nowrap|360 to 440 mV}} for logical high level, and termination of 45 Ω to ground or 90 Ω differential to match the data cable impedance.
* '''SuperSpeed (SS)''' adds two additional pairs of shielded twisted data wires (and new, mostly compatible expanded connectors) besides another grounding wire. These are dedicated to full-duplex SuperSpeed operation. The SuperSpeed link operates independently from the USB 2.0 channel and takes precedence on connection. Link configuration is performed using LFPS (Low Frequency Periodic Signaling, approximately at 20 MHz frequency), and electrical features include voltage de-emphasis at the transmitter side, and adaptive linear equalization on the receiver side to combat electrical losses in transmission lines, and thus the link introduces the concept of ''link training''.
* '''SuperSpeed+ (SS+)''' uses a new coding scheme with an increased signaling rate (Gen 2×1 mode) and/or the additional lane of USB-C (Gen 1×2 and Gen 2×2 modes).

A USB connection is always between an ''A'' end, a downstream-facing port (DFP) of either a ''host'' or a ''hub'', and a ''B'' end, the upstream-facing port (UFP) of either a ''peripheral device'' or a ''hub''. Historically, this was made clear by the fact that hosts had only Type-A and peripheral devices had only Type-B ports, and every compatible cable had one Type-A plug and one Type-B plug.

USB-C (Type-C) is a single connector that replaces all legacy Type-A and Type-B connectors, so when both sides are equipment with USB Type-C ports, normally the device's type defines which is the DFP and which is the UFP. Some devices, e.g. modern smart phones, can act as both. Consequently, the connected devices negotiate which is the ''host'' and which is the ''peripheral device''.

== Protocol layer ==
{{Main|USB (Communications)#Protocol layer}}
During USB communication, data is transmitted as [[Network packet|packets]]. Initially, all packets are sent from the host via the root hub, and possibly more hubs, to devices. Some of those packets direct a device to send some packets in reply.

== Transactions ==
{{Main|USB (Communications)#Transaction}}

The basic transactions of USB are:
* OUT transaction
* IN transaction
* SETUP transaction
* Control transfer exchange

== Related standards ==
[[File:USB Wireless certified Logo.svg|thumb|upright=0.5|The Wireless USB logo]]

=== Media Agnostic USB ===
The USB Implementers Forum introduced the Media Agnostic USB (MA-USB) v.1.0 wireless communication standard based on the USB protocol on 29 July 2015. [[Wireless USB]] is a cable-replacement technology, and uses [[ultra-wideband]] [[wireless technology]] for data rates of up to 480 Mbit/s.<ref>{{cite web |url=https://www.usb.org/document-library/media-agnostic-usb-v10a-spec-and-adopters-agreement |title=Media Agnostic USB v1.0a Spec and Adopters Agreement |website=usb.org |access-date=21 July 2021 |archive-date=31 July 2021 |archive-url=https://web.archive.org/web/20210731194632/https://www.usb.org/document-library/media-agnostic-usb-v10a-spec-and-adopters-agreement |url-status=live }}</ref>

The USB-IF used WiGig Serial Extension v1.2 specification as its initial foundation for the MA-USB specification and is compliant with SuperSpeed USB (3.0 and 3.1) and Hi-Speed USB (USB 2.0). Devices that use MA-USB will be branded as "Powered by MA-USB", provided the product qualifies its certification program.<ref>{{cite web |url=https://www.tweaktown.com/news/36420/usb-if-releases-final-specification-of-media-agnostic-usb/index.html |title=USB-IF releases final specification of Media Agnostic USB |work=tweaktown.com |last=Shaikh |first=Roshan Ashraf |date=3 November 2020 |access-date=21 July 2021 |archive-date=15 March 2021 |archive-url=https://web.archive.org/web/20210315204103/https://www.tweaktown.com/news/36420/usb-if-releases-final-specification-of-media-agnostic-usb/index.html |url-status=live }}</ref>

=== InterChip USB ===
{{Main|InterChip USB}}
InterChip USB is a chip-to-chip variant that eliminates the conventional transceivers found in normal USB. The HSIC [[physical layer]] uses about 50% less power and 75% less [[printed circuit board|board]] area compared to USB 2.0.<ref>{{cite web |title= Interchip Connectivity: HSIC, UniPro, HSI, C2C, LLI... oh my! |url= http://info.arteris.com/blog/bid/59433/Interchip-Connectivity-HSIC-UniPro-HSI-C2C-LLI-oh-my |first=Kurt |last=Shuler |date=31 March 2011 |access-date= 24 June 2011 |website= Arteris IP |url-status=live |archive-url= https://web.archive.org/web/20110619022557/http://info.arteris.com/blog/bid/59433/Interchip-Connectivity-HSIC-UniPro-HSI-C2C-LLI-oh-my |archive-date= 19 June 2011}}</ref> It is an alternative standard to [[Serial Peripheral Interface|SPI]] and [[I2C]].

=== USB-C ===
{{Main|USB-C}}
USB-C (officially ''USB Type-C'') is a standard that defines a new connector, and several new connection features. Among them it supports ''Alternate Mode'', which allows transporting other protocols via the USB-C connector and cable. This is commonly used to support the [[DisplayPort]] or [[HDMI]] protocols, which allows connecting a display, such as a [[computer monitor]] or [[television set]], via USB-C.

All other connectors are not capable of two-lane operations (Gen 1×2 and Gen 2×2) in USB 3.2, but can be used for one-lane operations (Gen 1×1 and Gen 2×1).<ref name="Black Box">{{cite web |title=USB 3.2 and Beyond |url=https://www.blackbox.co.uk/gb-gb/page/29254/Resources/Technical-Resources/Black-Box-Explains/USB(Universal-Serial-Bus)/USB-Connectivity-USB-32-and-Beyond |website=Black Box |access-date=4 March 2023}}</ref>

=== DisplayLink ===
{{Main|DisplayLink}}
DisplayLink is a technology which allows multiple displays to be connected to a computer via USB. It was introduced around 2006, and before the advent of Alternate Mode over USB-C it was the only way to connect displays via USB. It is a proprietary technology, not standardized by the USB Implementers Forum and typically requires a separate [[device driver]] on the computer.

== Comparisons with other connection methods ==
=== FireWire (IEEE 1394) ===
At first, USB was considered a complement to FireWire ([[IEEE 1394]]) technology, which was designed as a high-bandwidth serial bus that efficiently interconnects peripherals such as disk drives, audio interfaces, and video equipment. In the initial design, USB operated at a far lower data rate and used less sophisticated hardware. It was suitable for small peripherals such as keyboards and pointing devices.

The most significant technical differences between FireWire and USB include:

* USB networks use a [[star network|tiered-star]] topology, while IEEE 1394 networks use a [[tree network|tree]] topology.
* USB 1.0, 1.1, and 2.0 use a "speak-when-spoken-to" protocol, meaning that each peripheral communicates with the host when the host specifically requests communication. USB 3.0 allows for device-initiated communications towards the host. A FireWire device can communicate with any other node at any time, subject to network conditions.
* A USB network relies on a single host at the top of the tree to control the network. All communications are between the host and one peripheral. In a FireWire network, any capable node can control the network.
* USB runs with a 5 [[Volts|V]] power line, while FireWire supplies 12 V and theoretically can supply up to 30 V.
* Standard USB hub ports can provide from the typical 500 mA/2.5 W of current, only 100 mA from non-hub ports. USB 3.0 and USB On-The-Go supply 1.8 A/9.0 W (for dedicated battery charging, 1.5 A/7.5 W full bandwidth or 900 mA/4.5 W high bandwidth), while FireWire can in theory supply up to 60 watts of power, although 10 to 20 watts is more typical.

These and other differences reflect the differing design goals of the two buses: USB was designed for simplicity and low cost, while FireWire was designed for high performance, particularly in time-sensitive applications such as audio and video. Although similar in theoretical maximum signaling rate, FireWire 400 is faster than USB 2.0 high-bandwidth in real-use,<ref>{{cite web|title=FireWire vs. USB 2.0|url=http://www.qimaging.com/support/pdfs/firewire_usb_technote.pdf|publisher=QImaging|access-date=20 July 2010|url-status=live|archive-url=https://web.archive.org/web/20101011050049/http://www.qimaging.com/support/pdfs/firewire_usb_technote.pdf|archive-date=11 October 2010}}</ref> especially in high-bandwidth use such as external hard drives.<ref>{{cite web |url= http://www.cwol.com/firewire/firewire-vs-usb.htm |title= FireWire vs. USB 2.0 – Bandwidth Tests |access-date= 25 August 2007 |url-status=live |archive-url= https://web.archive.org/web/20070812045719/http://www.cwol.com/firewire/firewire-vs-usb.htm |archive-date= 12 August 2007}}</ref><ref>{{cite web |url=https://www.pricenfees.com/digit-life-archives/usb-2-0-vs-firewire |title=USB 2.0 vs FireWire |publisher=Pricenfees |access-date=25 August 2007 |url-status=live |archive-url=https://web.archive.org/web/20161016063120/https://www.pricenfees.com/digit-life-archives/usb-2-0-vs-firewire |archive-date=16 October 2016}}</ref><ref>{{cite magazine |url=https://www.pcmag.com/article2/0,4149,847716,00.asp |title=The Great Interface-Off: FireWire Vs. USB 2.0 |magazine=PC Magazine |access-date=25 August 2007 |last=Metz |first=Cade |date=25 February 2003 |url-status=live |archive-url=https://web.archive.org/web/20070930190355/http://www.pcmag.com/article2/0,4149,847716,00.asp |archive-date=30 September 2007 }}</ref><ref>{{cite web|url=http://www.g4tv.com/techtvvault/features/39129/USB_20_Versus_FireWire_pg3.html|title=USB 2.0 Versus FireWire|access-date=25 August 2007|author=Heron, Robert|publisher=TechTV|url-status=live|archive-url=https://web.archive.org/web/20070929121843/http://www.g4tv.com/techtvvault/features/39129/USB_20_Versus_FireWire_pg3.html|archive-date=29 September 2007}}</ref> The newer FireWire 800 standard is twice as fast as FireWire 400 and faster than USB 2.0 high-bandwidth both theoretically and practically.<ref>{{cite web | url = http://www.usb-ware.com/firewire-vs-usb.htm | title = FireWire vs. USB 2.0 | publisher = USB Ware | access-date = 19 March 2007 | url-status=live | archive-url = https://web.archive.org/web/20070316072513/http://www.usb-ware.com/firewire-vs-usb.htm | archive-date = 16 March 2007}}</ref> However, FireWire's speed advantages rely on low-level techniques such as [[direct memory access]] (DMA), which in turn have created opportunities for security exploits such as the [[DMA attack]].

The chipset and drivers used to implement USB and FireWire have a crucial impact on how much of the bandwidth prescribed by the specification is achieved in the real world, along with compatibility with peripherals.<ref>{{cite web |url=http://www.anandtech.com/mb/showdoc.aspx?i=2602&p=15 |title=Firewire and USB Performance |access-date=1 February 2008 |last=Key |first=Gary |date=15 November 2005 |url-status=dead |archive-url=https://web.archive.org/web/20080423214619/http://www.anandtech.com/mb/showdoc.aspx?i=2602&p=15 |archive-date=23 April 2008}}</ref>

=== Ethernet ===
The ''IEEE 802.3af'', ''802.3at'', and ''802.3bt'' [[Power over Ethernet]] (PoE) standards specify more elaborate power negotiation schemes than powered USB. They operate at 48 V [[Direct current|DC]] and can supply more power (up to 12.95 W for ''802.3af'', 25.5 W for ''802.3at'', a.k.a. ''PoE+'', 71 W for ''802.3bt'', a.k.a. ''4PPoE'') over a cable up to 100 meters compared to USB 2.0, which provides 2.5 W with a maximum cable length of 5 meters. This has made PoE popular for [[Voice over IP]] telephones, [[security camera]]s, [[wireless access point]]s, and other networked devices within buildings. However, USB is cheaper than PoE provided that the distance is short and power demand is low.

[[Ethernet]] standards require electrical isolation between the networked device (computer, phone, etc.) and the network cable up to 1500 V AC or 2250 V DC for 60 seconds.<ref>{{cite web | url = http://standards.ieee.org/getieee802/download/802.3-2008_section1.pdf | title = 802.3, Section 14.3.1.1 | publisher = IEEE | url-status=dead | archive-url = https://web.archive.org/web/20101206030247/http://standards.ieee.org/getieee802/download/802.3-2008_section1.pdf | archive-date = 6 December 2010}}</ref> USB has no such requirement as it was designed for peripherals closely associated with a host computer, and in fact it connects the peripheral and host grounds. This gives Ethernet a significant safety advantage over USB with peripherals such as cable and DSL modems connected to external wiring that can assume hazardous voltages under certain fault conditions.<ref>{{cite web|date=8 March 2010|title=Powerbook Explodes After Comcast Plugs in Wrong Cable|url=http://consumerist.com/2006/12/powerbook-explodes-after-comcast-plugs-in-wrong-cable.html|url-status=dead|archive-url=https://web.archive.org/web/20100625052120/http://consumerist.com/2006/12/powerbook-explodes-after-comcast-plugs-in-wrong-cable.html|archive-date=25 June 2010|access-date=22 June 2010|publisher=Consumerist}}</ref><ref>{{Cite web|date=2021|title=Technical Note. Galvanic Isolation|url=https://www.isystem.com/files/content/downloads/documents/technical-notes/iSYSTEM_TN_Galvanic_Isolation.pdf#page=4|website=iSYSTEM|format=PDF|access-date=13 February 2022|archive-date=21 December 2021|archive-url=https://web.archive.org/web/20211221080208/https://www.isystem.com/files/content/downloads/documents/technical-notes/iSYSTEM_TN_Galvanic_Isolation.pdf#page=4|url-status=live}}</ref>

=== MIDI ===
The ''USB Device Class Definition for MIDI Devices'' transmits Music Instrument Digital Interface ([[MIDI]]) music data over USB.<ref>{{cite web |url=https://www.usb.org/sites/default/files/midi10.pdf |title=Universal Serial Bus Device Class Definition for MIDI Devices |website=usb.org |date=1 November 1999 |access-date=21 July 2021 |archive-date=2 November 2021 |archive-url=https://web.archive.org/web/20211102080622/https://www.usb.org/sites/default/files/midi10.pdf |url-status=live}}</ref> The MIDI capability is extended to allow up to sixteen simultaneous ''virtual MIDI cables'', each of which can carry the usual MIDI sixteen channels and clocks.

USB is competitive for low-cost and physically adjacent devices. However, Power over Ethernet and the [[MIDI]] plug standard have an advantage in high-end devices that may have long cables. USB can cause [[ground loop (electricity)|ground loop]] problems between equipment, because it connects ground references on both transceivers. By contrast, the MIDI plug standard and [[Ethernet]] have built-in isolation to {{gaps|500|V}} or more.

=== eSATA/eSATAp ===
The [[eSATA]] connector is a more robust [[SATA]] connector, intended for connection to external hard drives and SSDs. eSATA's transfer rate (up to 6 Gbit/s) is similar to that of USB 3.0 (up to 5 Gbit/s) and USB 3.1 (up to 10 Gbit/s). A device connected by eSATA appears as an ordinary SATA device, giving both full performance and full compatibility associated with internal drives.

eSATA does not supply power to external devices. This is an increasing disadvantage compared to USB. Even though USB 3.0's 4.5 W is sometimes insufficient to power external hard drives, technology is advancing, and external drives gradually need less power, diminishing the eSATA advantage. [[eSATAp]] (power over eSATA, a.k.a. ESATA/USB) is a connector introduced in 2009 that supplies power to attached devices using a new, backward compatible, connector. On a notebook eSATAp usually supplies only 5 V to power a 2.5-inch HDD/SSD; on a desktop workstation it can additionally supply 12 V to power larger devices including 3.5-inch HDD/SSD and 5.25-inch optical drives.

eSATAp support can be added to a desktop machine in the form of a bracket connecting the motherboard SATA, power, and USB resources.

eSATA, like USB, supports [[hot plugging]], although this might be limited by OS drivers and device firmware.

=== Thunderbolt ===
{{Main|Thunderbolt (interface)}}
Thunderbolt combines [[PCI Express]] and [[DisplayPort]] into a new serial data interface. Original Thunderbolt implementations have two channels, each with a transfer speed of 10 Gbit/s, resulting in an aggregate unidirectional bandwidth of 20 Gbit/s.<ref>{{cite web |url=https://thunderbolttechnology.net/tech/how-it-works |title=How Thunderbolt Technology Works: Thunderbolt Technology Community |website=ThunderboltTechnology.net |access-date=22 January 2014 |url-status=live |archive-url=https://web.archive.org/web/20140210063142/https://thunderbolttechnology.net/tech/how-it-works |archive-date=10 February 2014 }}</ref>

[[Thunderbolt 2]] uses link aggregation to combine the two 10 Gbit/s channels into one bidirectional 20 Gbit/s channel.<ref>{{cite web |title=What you need to know about Thunderbolt 2 |url=https://www.macworld.com/article/222636/what-you-need-to-know-about-thunderbolt-2.html#:~:text=What%20is%20Thunderbolt%202%3F,20%20Gbps%20bi%2Ddirectional%20channel. |first=Jim |last=Galbraith |date=2 January 2014 |access-date=18 June 2021 |website=Macworld |publisher=IDG Communications, Inc. |archive-date=24 June 2021 |archive-url=https://web.archive.org/web/20210624202741/https://www.macworld.com/article/222636/what-you-need-to-know-about-thunderbolt-2.html#:~:text=What%20is%20Thunderbolt%202%3F,20%20Gbps%20bi%2Ddirectional%20channel. |url-status=live }}</ref>

[[Thunderbolt 3]] and [[Thunderbolt 4]] use [[USB-C]].<ref>{{cite web|url=https://www.cnet.com/news/thunderbolt-3-and-usb-type-c-join-forces-for-one-port-to-rule-them-all/|title=One port to rule them all: Thunderbolt 3 and USB Type-C join forces|archive-url=https://web.archive.org/web/20150602195337/http://www.cnet.com/news/thunderbolt-3-and-usb-type-c-join-forces-for-one-port-to-rule-them-all/|archive-date=2 June 2015|url-status=live|access-date=2 June 2015}}</ref><ref>{{cite web |url=https://www.engadget.com/2015/06/02/thunderbolt-3-usb-c/ |title=Thunderbolt 3 is twice as fast and uses reversible USB-C |date=2 June 2015 |access-date=2 June 2015 |url-status=live |archive-url=https://web.archive.org/web/20150603000428/http://www.engadget.com/2015/06/02/thunderbolt-3-usb-c/ |archive-date=3 June 2015 }}</ref><ref>{{cite web |url=https://arstechnica.com/gadgets/2015/06/thunderbolt-3-embraces-usb-type-c-connector-doubles-bandwidth-to-40gbps/ |title=Thunderbolt 3 embraces USB Type-C connector, doubles bandwidth to 40 Gbps |author=Sebastian Anthony |date=2 June 2015|website=Ars Technica |access-date=2 June 2015 |url-status=live |archive-url=https://web.archive.org/web/20150609183247/https://arstechnica.com/gadgets/2015/06/thunderbolt-3-embraces-usb-type-c-connector-doubles-bandwidth-to-40gbps/ |archive-date=9 June 2015 }}</ref> Thunderbolt 3 has two physical 20 Gbit/s bi-directional channels, aggregated to appear as a single logical 40 Gbit/s bi-directional channel. Thunderbolt 3 controllers can incorporate a USB 3.1 Gen 2 controller to provide compatibility with USB devices. They are also capable of providing DisplayPort Alternate Mode as well as DisplayPort over USB4 Fabric, making the function of a Thunderbolt 3 port a superset of that of a USB 3.1 Gen 2 port.

DisplayPort Alternate Mode 2.0: USB4 (requiring USB-C) requires that hubs support DisplayPort 2.0 over a USB-C Alternate Mode. DisplayPort 2.0 can support 8K resolution at 60 Hz with HDR10 color.<ref name="displayport">{{cite web |title=New DisplayPort spec enables 16K video over USB-C |url=https://www.theverge.com/2020/4/30/21242445/vesa-displayport-alt-mode-2-0-usb-4-4k-144hz-hdr-8k-16k-displays |first=Jon |last=Porter |date=30 April 2020 |access-date=18 June 2021 |website=The Verge |publisher=Vox Media, LLC |archive-date=15 April 2021 |archive-url=https://web.archive.org/web/20210415051447/https://www.theverge.com/2020/4/30/21242445/vesa-displayport-alt-mode-2-0-usb-4-4k-144hz-hdr-8k-16k-displays |url-status=live }}</ref> DisplayPort 2.0 can use up to 80 Gbit/s, which is double the amount available to USB data, because it sends all the data in one direction (to the monitor) and can thus use all eight data wires at once.<ref name="displayport"/>

After the specification was made royalty-free and custodianship of the Thunderbolt protocol was transferred from Intel to the USB Implementers Forum, Thunderbolt 3 has been effectively implemented in the USB4 specification – with compatibility with Thunderbolt 3 optional but encouraged for USB4 products.<ref>{{cite web|title=USB4 Thunderbolt3 Compatibility Requirements Specification|url=https://www.usb.org/sites/default/files/USB4%E2%84%A2%20Thunderbolt3%E2%84%A2%20Compatibility%20Requirements%20Specification%20Rev%201.0%20-%2020210129_0.pdf|date=January 2021|access-date=1 January 2021|website=USB|publisher= USB Implementers Forum |archive-date=19 October 2021|archive-url=https://web.archive.org/web/20211019074211/https://usb.org/sites/default/files/USB4%E2%84%A2%20Thunderbolt3%E2%84%A2%20Compatibility%20Requirements%20Specification%20Rev%201.0%20-%2020210129_0.pdf|url-status=live}}</ref>

== Interoperability ==
{{Main|USB-to-serial adapter}}
Various [[protocol converter]]s are available that convert USB data signals to and from other communications standards.

== Security threats ==
{{See also|USB flash drive security}}
Due to the USB standard's [[Plug and play|plug-and-play]] nature, host computers are vulnerable to USB devices containing malicious software. It is possible to create a device that looks like a flash drive, but when plugged in, simulates a keyboard and types malicious commands. For example, on a computer running [[Microsoft Windows]], the device can wait a set amount of time, then open [[PowerShell]] and download a [[malware]] script. The attack is called a [[BadUSB]] attack.<ref>{{Cite web |last=Goodin |first=Dan |date=July 31, 2014 |title=This thumbdrive hacks computers. 'BadUSB' exploit makes devices turn 'evil' |language=en-us |website=[[Ars Technica]] |url=https://arstechnica.com/information-technology/2014/07/this-thumbdrive-hacks-computers-badusb-exploit-makes-devices-turn-evil/ |access-date=2021-09-07 |url-status=live|archive-url=https://web.archive.org/web/20170909170957/https://arstechnica.com/information-technology/2014/07/this-thumbdrive-hacks-computers-badusb-exploit-makes-devices-turn-evil/ |archive-date=2017-09-09 }}</ref><ref>{{cite magazine |last=Greenberg |first=Andy |date=July 31, 2014 |title=Why the Security of USB Is Fundamentally Broken |language=en-US |magazine=Wired |issn=1059-1028 |url=https://www.wired.com/2014/07/usb-security/ |access-date=2021-09-07}}</ref>

Another malicious device is a [[USB killer]], which sends high voltage pulses across the data lines, destroying or damaging whatever it is plugged into.<ref name="tomshardware">{{Cite web |url=http://www.tomshardware.com/news/usb-killer-2.0-power-surge-attack,32669.html |title='USB Killer V2.71' Shows That Most USB-Enabled Devices Are Vulnerable To Power Surge Attacks |last=Armasu |first=Lucian |date=2017-08-12 |website=[[Tom's Hardware]]}}</ref><ref name="DeccanChronicle">{{Cite web |url=https://www.deccanchronicle.com/technology/in-other-news/120916/usb-killer-a-device-that-can-destroy-a-pc-in-seconds.html |title=USB Killer: A device that can destroy a PC in seconds |date=2017-08-12 |newspaper=[[Deccan Chronicle]]}}</ref><ref name="independent">{{Cite web |url=https://www.independent.co.uk/life-style/gadgets-and-tech/news/russian-computer-researcher-creates-a-usb-killer-thumb-drive-that-will-fry-your-computer-in-seconds-a6696511.html |title=Russian computer researcher creates a USB killer thumb drive that will fry your computer in seconds |last=Bolton |first=Doug |date=2017-08-12 |newspaper=[[The Independent]]}}</ref>

In versions of [[Microsoft Windows]] before [[Windows XP]], Windows would automatically run a script (if present) on certain devices via [[AutoRun]], one of which are USB mass storage devices, which may contain malicious software.<ref>{{cite web |url=https://www.samlogic.net/articles/autorun-usb-flash-drive.htm |title=Using AutoRun with a USB Flash Drive (USB stick) |website=Positive Technologies |date=25 June 2022 |access-date=26 July 2022 |archive-date=26 April 2022 |archive-url=https://web.archive.org/web/20220426181327/https://www.samlogic.net/articles/autorun-usb-flash-drive.htm |url-status=live }}</ref>

It is possible to gain full system control by hacking a USB controller.<ref>{{Cite web |date=2025-01-12 |title=Apple devices at risk after security researcher hacks ACE3 USB-C controller |url=https://siliconangle.com/2025/01/12/apple-devices-risk-security-researcher-hacks-ace3-usb-c-controller/ |access-date=2025-11-06 |website=SiliconANGLE |language=en-US}}</ref>

== See also ==
{{Portal|Electronics}}

=== USB ===
{{Div col|colwidth=24em}}
* [[USB communications]]
* [[USB hardware]]
* [[USB-C]]
* [[USB hub]]
* [[Extensible Host Controller Interface]] (XHCI)
* {{section link|List of interface bit rates|Peripheral}}
* [[WebUSB]]
{{Div col end}}

=== Derived and related standards ===
{{Div col|colwidth=24em}}
* [[DockPort]]
* [[LIO Target]]
* [[Media Transfer Protocol]]
* [[Mobile High-Definition Link]]
* [[Thunderbolt (interface)]]
* [[Windows Easy Transfer]]
{{Div col end}}

==Notes==
{{reflist|group=note}}

== References ==
{{Reflist |refs=
<ref name="USBDataPerformance">{{Cite web |title=USB Data Performance, Language Usage Guidelines from USB-IF |url=https://usb.org/sites/default/files/usb_data_performance_language_usage_guidelines_september_2022.pdf |website=USB Implementers Forum |location=Beaverton, OR, USA |access-date=2 September 2022 |archive-date=1 October 2022 |archive-url=https://web.archive.org/web/20221001115816/https://www.usb.org/sites/default/files/usb_data_performance_language_usage_guidelines_september_2022.pdf |url-status=dead}}</ref>
<ref name=USB30Spec>{{cite web | url=http://www.usb.org/developers/docs/documents_archive/usb_30_spec_070113.zip |title=Universal Serial Bus 3.0 Specification |date=6 June 2011 |website=USB Implementers Forum |publisher=[[Hewlett-Packard Company]] [[Intel Corporation]] [[Microsoft Corporation]] [[NEC Corporation]] [[ST-Ericsson]] [[Texas Instruments]] |location=Beaverton, OR, USA |format=[[ZIP (file format)|ZIP]] |url-status=live |archive-url=https://web.archive.org/web/20140519092924/http://www.usb.org/developers/docs/documents_archive/usb_30_spec_070113.zip |archive-date=19 May 2014}} {{cite web |title=Universal Serial Bus 3.0 Specification |url=http://www.gaw.ru/pdf/interface/usb/USB%203%200_english.pdf |date=12 November 2008 |access-date=29 December 2012 |via= www.gaw.ru |archive-date=6 October 2012 |archive-url=https://web.archive.org/web/20121006160059/http://www.gaw.ru/pdf/interface/usb/USB%203%200_english.pdf |url-status= live }}</ref>
<ref name="xmos2015">{{Cite web
|url=http://www.epsglobal.com/downloads/XMOS/Why-do-you-need-USB-Audio-Class-2.pdf
|title=Why do you need USB Audio Class 2? |last=Strong |first=Laurence |date=2015 |publisher=XMOS |url-status=dead |archive-url=https://web.archive.org/web/20171124080752/http://www.epsglobal.com/downloads/XMOS/Why-do-you-need-USB-Audio-Class-2.pdf |archive-date=24 November 2017 |access-date=11 December 2020 |quote=In applications where streaming latency is important, UAC2 offers up to an 8x reduction over UAC1. ... Each clocking method has pros and cons and best-fit applications.}}</ref>
}}

== Further reading ==
* {{Cite book | first = Jan | last = Axelson | date = 1 September 2006 | title = USB Mass Storage: Designing and Programming Devices and Embedded Hosts | publisher = [[Lakeview Research]] | edition = 1st | isbn = 978-1-931-44804-8 | url = https://archive.org/details/isbn_9781931448048 | url-access = registration }}
* {{Cite book| first = Jan | last = Axelson | author-mask = 3 | date = 1 December 2007 | title = Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems | publisher = Lakeview Research | edition = 2nd | isbn = 978-1-931-44806-2 | url = http://janaxelson.com/spc.htm}}
* {{Cite book| first = Jan | last = Axelson | author-mask = 3 | year = 2015 | title = USB Complete: The Developer's Guide | publisher = Lakeview Research | edition = 5th | isbn = 978-1-931448-28-4 | url = http://janaxelson.com/usbc.htm}}
* {{Cite book| first = John | last = Hyde | date = February 2001 | title = USB Design by Example: A Practical Guide to Building I/O Devices | publisher = [[Intel Press]] | edition = 2nd | isbn = 978-0-970-28465-5 | url = http://www.intel.com/intelpress/usb/}}
* {{Cite journal|title=Debugging USB 2.0 for Compliance: It's Not Just a Digital World|publisher=Keysight|series=Technologies Application Note|issue=1382–3|journal=Keysight Technologies|url=http://literature.cdn.keysight.com/litweb/pdf/5988-4794EN.pdf}}

== External links ==
{{Commons|Universal Serial Bus}}
{{Wikibooks|Serial Programming:USB Technical Manual|USB connectors}}

=== General overview ===
* {{cite web |url=https://www.fastcompany.com/3060705/an-oral-history-of-the-usb |title=The unlikely origins of USB, the port that changed everything |author=Johnson |first=Joel |publisher=[[Fast Company]] |date=29 May 2019}}
* {{cite AV media |url = https://www.youtube.com/watch?v=36CKsP9YQ1E |title = Why Does USB Keep Changing? |first=Peter |last=Leigh |date = 24 May 2020 |medium = video }}
* {{cite news |last=Parikh |first=Bijal |title=USB (Universal Serial Bus): An Overview |url=https://www.engineersgarage.com/usb-universal-serial-bus-an-overview/ |access-date=7 May 2022 |work=Engineers Garage |publisher=WTWH Media}}
* {{cite AV media |url = https://www.youtube.com/watch?v=PctX3kcTj5U |title = Explaining USB: From 1.0 to USB4 V2.0 (ExplainingComputers)|first=Christopher |last=Barnatt |date = 25 September 2022 |medium = video }}

=== Technical documents ===
* {{cite web |url = https://www.usb.org/ |title = USB Implementers Forum (USB-IF) |website = USB.org }}
* {{cite web |url = https://www.usb.org/documents |title = USB Document Library (USB 3.2, USB 2.0, Wireless USB, USB-C, USB Power Delivery) |website = USB.org }}
* {{cite web |url = http://stuff.mit.edu/afs/sipb/contrib/doc/specs/protocol/usb/UHCI11D.PDF |title = Universal Host Controller Interface (UHCI) |publisher = [[Intel]] |via=mit.edu}}
* {{cite web |url = http://pinoutsguide.com/Slots/usb_3_0_connector_pinout.shtml |title = USB 3.0 Standard-A, Standard-B, Powered-B connectors |website=Pinouts guide |archive-url=https://web.archive.org/web/20160514121804/http://pinoutsguide.com/Slots/usb_3_0_connector_pinout.shtml |archive-date=14 May 2016}}
* {{cite web |url = https://www.electronicdesign.com/boards/how-create-and-program-usb-devices |title = How to Create and Program USB Devices |first=Henk |last=Muller |publisher = [[Electronic Design]] |date = July 2012 }}
* {{cite web |url = https://usb.org/sites/default/files/bwpaper2.pdf |title = An Analysis of Throughput Characteristics of Universal Serial Bus |first=John |last=Garney |date = June 1996 }}
* {{cite web |url=https://engineering.biu.ac.il/files/engineering/shared/PE_project_book_0.pdf |title=USB 2.0 Protocol Engine |first1=Razi |last1=Hershenhoren |first2=Omer |last2=Reznik |date=October 2010 |access-date=30 January 2019 |archive-date=4 August 2020 |archive-url=https://web.archive.org/web/20200804030543/https://engineering.biu.ac.il/files/engineering/shared/PE_project_book_0.pdf |url-status=dead }}
* [[IEC]] 62680 (Universal Serial Bus interfaces for data and power):
** [https://webstore.iec.ch/publication/23281 IEC 62680-1.1:2015{{dash}}Part 1-1: Common components{{dash}}USB Battery Charging Specification, Revision 1.2]
** [https://webstore.iec.ch/publication/60944 IEC 62680-1-2:2018{{dash}}Part 1-2: Common components{{dash}}USB Power Delivery specification]
** [https://webstore.iec.ch/publication/61599 IEC 62680-1-3:2018{{dash}}Part 1-3: Common components{{dash}}USB Type-C Cable and Connector Specification]
** [https://webstore.iec.ch/publication/60748 IEC 62680-1-4:2018{{dash}}Part 1-4: Common components{{dash}}USB Type-C Authentication Specification]
** [https://webstore.iec.ch/publication/23313 IEC 62680-2-1:2015{{dash}}Part 2-1: Universal Serial Bus Specification, Revision 2.0]
** [https://webstore.iec.ch/publication/23282 IEC 62680-2-2:2015{{dash}}Part 2-2: Micro-USB Cables and Connectors Specification, Revision 1.01]
** [https://webstore.iec.ch/publication/23283 IEC 62680-2-3:2015{{dash}}Part 2-3: Universal Serial Bus Cables and Connectors Class Document Revision 2.0]
** [https://webstore.iec.ch/publication/29943 IEC 62680-3-1:2017{{dash}}Part 3-1: Universal Serial Bus 3.1 Specification]

{{List of IEC standards}}
{{Basic computer components}}
{{Computer bus}}
{{DC power delivery standards}}
{{USB}}
{{Solid-state drive}}

{{Authority control}}

[[Category:USB| ]]
[[Category:American inventions]]
[[Category:Computer buses]]
[[Category:Computer connectors]]
[[Category:Computer-related introductions in 1996]]
[[Category:Japanese inventions]]
[[Category:Physical layer protocols]]
[[Category:Serial buses]]
== Примечания ==
<references group="rem"/>

Transistor-transistor logic

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Synchronous serial communication

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{{Short description|Serial communication with clock signal}}

'''Synchronous serial communication''' describes a [[serial communication]] [[communication protocol|protocol]], "In synchronous transmission, groups of bits are combined into frames, and frames are sent continuously with or without data to be transmitted."<ref>{{cite book |last1=Dawoud |first1=Dawoud Shenouda |last2=Dawoud |first2=Peter |title=Serial Communication Protocols and Standards |date=2020 |publisher=River Publishers |location=New York |isbn=9781003339496 |page=10 |edition=1st |doi=10.1201/9781003339496 |url=https://www.taylorfrancis.com/books/mono/10.1201/9781003339496/serial-communication-protocols-standards-dawoud-shenouda-dawoud-peter-dawoud |access-date=24 May 2025}}</ref>

Synchronous communication requires that the [[Clock signal|clocks]] in the transmitting and receiving devices are ''synchronized'' – running at the same rate – so the receiver can sample the signal at the same time intervals used by the transmitter. No start or stop bits are required. For this reason, "synchronous communication permits more information to be passed over a circuit per unit time"<ref>{{cite book|last=IBM Corporation|title=Data Communications Primer|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/datacomm/C29-1668-0_datacommPrimer.pdf}}</ref> than [[asynchronous serial communication]]. Over time the transmitting and receiving clocks will tend to drift apart, requiring ''resynchronization''.

Synchronous RS-232 used additional pins on the DB-25 cable: the DCE (generally the modem or other peripheral) provided two clock signals to the DTE (generally the host computer or terminal), transmitter clock (pin 15, TCK) and receiver clock (pin 17, RCK). Some systems supported an alternative mode of operation in which the transmitter clock signal was provided by the DTE instead, called transmitter timing (pin 24, TT).<ref>{{Cite journal |last=Kasperek |first=Gabriel |date=September 1983 |title=Modems: simple techniques for isolating common faults |url=https://books.google.com/books?id=7xNVAAAAMAAJ&pg=PA107 |journal=Data Communications |language=en |publisher=McGraw-Hill |pages=107}}</ref> Note the smaller DE-9 connector commonly adopted in later systems does not have these additional signal lines, and hence cannot be used with synchronous RS-232.

==Byte-oriented protocols==
Early synchronous protocols were [[byte-oriented protocol]]s, where synchronization was maintained by transmitting a sequence of [[synchronous idle]] characters when the line was not actively transmitting data or [[Transparency (telecommunication)|transparently]] within a long transmission block. A certain number of idles were sent prior to each transmission. The IBM [[Binary Synchronous Communications|''Binary Synchronous protocol'']] (Bisync) is still in use, Other examples of byte-oriented protocols are IBM's ''[[Synchronous transmit-receive]]'' (STR), and ''[[Digital Data Communications Message Protocol]]'' (DDCMP) from [[Digital Equipment Corporation]]. Other computer manufacturers often offered similar protocols, differing mainly in small details.

==Bit-oriented protocols==
[[Bit-oriented protocol]]s are synchronous protocols that view the transmitted data as a stream of bits with no semantics, or meaning. Control codes are defined in terms of bit sequences instead of characters. Synchronization is maintained on an idle line by transmitting a predefined sequence of bits. ''[[Synchronous Data Link Control]]'' (SDLC) specifies that a station continue transmitting a sequence of '1' bits on an idle line.<ref>{{cite book|last=IBM Corporation|title=IBM Synchronous Data Link Control General Information .|year=1979|url=http://bitsavers.informatik.uni-stuttgart.de/pdf/ibm/datacomm/GA27-3093-2_SDLC_General_Information_Mar79.pdf}}</ref> Data to be transmitted on an idle line is prefixed with a special bit sequence '01111110'b, called a ''flag''. SDLC was the first bit-oriented protocol developed, and it was later adopted by the [[International Organization for Standardization]] (ISO) as ''[[High-Level Data Link Control]]'' (HDLC). Other examples of bit-oriented protocols are ''Logical Link Control'' (LLC)—[[IEEE 802.2]], and ANSI ''[[Advanced Data Communication Control Procedures]]'' (ADCCP).

==References==
{{Reflist}}

==See also==
*[[Asynchronous serial communication]]
*[[Comparison of synchronous and asynchronous signalling]]
*[[Iteration]]
*[[Serial communication]]

[[Category:Synchronization]]
[[Category:Data transmission]]
[[Category:Physical layer protocols]]

Synchronous Data Link Control

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{{Other uses|SDLC (disambiguation){{!}}SDLC}}
{{Short description|Computer communications protocol from IBM's Systems Network Architecture (SNA)}}
{{Infobox networking protocol
| title = Synchronous Data Link Control
| logo =
| logo alt =
| image =
| image alt =
| caption =
| is stack =
| abbreviation = SDLC
| purpose = Data framing
| developer = IBM
| date = {{Start date and age|1974| | }}
| based on =
| influenced =
| osilayer = [[Data link layer]]
| ports =
| rfcs =
| hardware =
}}

'''Synchronous Data Link Control''' ('''SDLC''') is a [[computer]] [[serial communication|serial]] [[communications protocol]] first introduced by [[IBM]] as part of its [[Systems Network Architecture]] (SNA). SDLC is used as layer 2, the [[data link layer]], in the SNA [[protocol stack]]. It supports multipoint links as well as error correction. It also runs under the assumption that an SNA header is present after the SDLC header.<ref>{{harv|Odom|2004}}.</ref> SDLC was mainly used by [[IBM mainframe]] and midrange systems; however, implementations exist on many platforms from many vendors. In the United States and Canada, SDLC can be found in traffic control cabinets.<ref>{{harv|ITS|2006}}.</ref> SDLC was released in 1975,<ref name=PCLT>[http://pclt.cis.yale.edu/pclt/COMM/SDLC.HTM PC Lube and Tune], accessed 15. October 2009.</ref> based on work done for [[IBM]] in the early 1970s.<ref name="hist">{{harv|Friend|1988|p=188}}.</ref>

SDLC operates independently on each communications link in the network and can operate on [[point-to-point (telecommunications)|point-to-point]] [[Point-to-multipoint communication (telecommunications)|multipoint]] or [[Current loop|loop]] facilities, on switched or dedicated, [[Two-wire circuit|two-wire]] or [[Four-wire circuit|four-wire]] circuits, and with [[full-duplex]] and [[half-duplex]] operation.<ref>{{harv|Pooch|1983|p=302}}.</ref> A unique characteristic of SDLC is its ability to mix half-duplex secondary stations with full-duplex primary stations on four-wire circuits, thus reducing the cost of dedicated facilities.<ref>{{harv|Pooch|1983|p=303}}.</ref>

This [[de facto]] standard has been adopted by [[International Organization for Standardization|ISO]] as [[High-Level Data Link Control]] (HDLC) in 1979<ref name="hist"/> and by [[ANSI]] as [[Advanced Data Communication Control Procedures]] (ADCCP). The latter standards added features such as the [[Asynchronous Balanced Mode]], frame sizes that did not need to be multiples of bit-octets, but also removed some of the procedures and messages (such as the TEST message).<ref>{{harv|Friend|1988|p=191}}.</ref>

[[Intel]] used SDLC as a base protocol for [[BITBUS]], still popular in Europe as [[fieldbus]] and included support in several controllers (i8044/i8344, i80152). The 8044 controller is still in production by third-party vendors. Other vendors putting hardware support for SDLC (and the slightly different HDLC) into communication controller chips of the 1980s included [[Zilog]], [[Motorola]], and [[National Semiconductor]]. As a result, a wide variety of equipment in the 1980s used it and it was very common in the mainframe-centric corporate networks which were the norm in the 1980s. The most common alternatives for SNA with SDLC were probably [[DECnet]] with [[Digital Data Communications Message Protocol]] (DDCMP), Burroughs Network Architecture (BNA) with Burroughs Data Link Control (BDLC), and [[ARPANET]] with [[Interface Message Processors|IMPs]].<ref>{{harv|Pooch|1983|pp=309–321}}.</ref>

== Differences between SDLC and HDLC ==
HDLC is mostly an extension of SDLC,{{r|GA27-3093-3|p=69–72}} but some features were deleted or renamed.

=== HDLC features not in SDLC ===
Features present in HDLC, but not SDLC, are:
* frames not a multiple of 8 bits long are illegal in SDLC, but optionally legal in HDLC.
* HDLC optionally allows addresses more than 1 byte long.
* HDLC has an option for a 32-bit [[frame check sequence]].
* asynchronous response mode, and the associated SARM and SARME U frames,
* asynchronous balanced mode, and the associated SABM and SABME U frames,
* and several other frame types created for HDLC:
** the selective reject (SREJ) S frame,
** the reset (RSET) command, and
** the nonreserved (NR0 through NR3) U frames.
Also not in SDLC are later HDLC extensions in ISO/IEC 13239 such as:
* 15- and 31-bit sequence numbers,
* the set mode (SM) U frame,
* 8-bit frame check sequence,
* a frame format field preceding the address,
* an information field in mode set U frames, and
* the "unnumbered information with header check" (UIH) U frame.


=== Naming differences ===
HDLC renamed some SDLC frames. The HDLC names were incorporated into later versions of SDLC:<ref name=GA27-3093-3>{{cite tech report |url=http://www.textfiles.com/bitsavers/pdf/ibm/datacomm/GA27-3093-3_SDLC_Concepts_Jun86.pdf |title=Synchronous Data Link Control: Concepts |edition=4th |date=June 1986 |id=Document No. GA27-3093-3 |author=IBM Communication Products Division}}</ref>{{Rp|73}}
{|class=wikitable
!colspan=2| Original name ||colspan=2| New name
|-
| NSA || Nonsequenced acknowledge || UA || Unnumbered acknowledge
|-
| NSI || Nonsequenced information || UI || Unnumbered information
|-
| NSP || Nonsequenced poll || UP || Unnumbered poll
|-
| ROL || Request online || DM || Disconnected mode
|-
| CMDR || Command reject || FRMR || Frame reject
|-
| RQI || Request initialization mode || RIM || Request initialization mode
|-
| RQD || Request disconnect || RD || Request disconnect
|}

=== HDLC extensions added to SDLC ===
Some features were added in HDLC, and subsequently added back to later versions of SDLC.
* Extended (modulo-128) sequence numbers and the corresponding SNRME U frame, were added to SDLC after the publication of the HDLC standard.

=== SDLC features not in HDLC ===
Two U frames in SDLC which do not exist in HDLC are:
* BCN (Beacon): When a secondary loses carrier (stops receiving any signal) from the primary, it begins transmitting a stream of "beacon" responses, identifying the location of the communication failure. This is particularly useful in SDLC loop mode.
* CFGR (Configure for test) command and response: The CFGR command contains a 1-byte payload which identifies some special diagnostic operation to be performed by the secondary.{{R|GA27-3093-3|p=47–49}} The least significant bit indicates that the diagnostic mode should start (1) or stop (0). A payload byte of 0 stops all diagnostic modes. The secondary echoes the byte in its response.
** 0: Stop all diagnostic modes.
** 2 (off)/3 (on): Beacon test. Disable all output, causing the next recipient to lose carrier (and begin beaconing).
** 4 (off)/5 (on): [[Monitor mode]]. Disable all frame generation, becoming silent, but do not stop carrier or loop mode operation.
** 8 (off)/9 (on): Wrap mode. Enter local loopback, connecting the secondary's input to its own output for the duration of the test.
** 10 (off)/11 (on): Self-test. Perform local diagnostics. CFGR response is delayed until the diagnostics complete, at which time the response is 10 (self-test failed) or 11 (self-test successful).
** 12 (off)/13 (on): Modified link test. Rather than echoing TEST commands verbatim, generate a TEST response consisting of a number of copies of the first byte of the TEST command.
Several U frames are almost entirely unused in HDLC, existing primarily for SDLC compatibility:
* Initialization mode, and the associated RIM and SIM U frames, are so vaguely defined in HDLC as to be useless, but are used by some peripherals in SDLC.
* Unnumbered poll (UP) is almost never used in HDLC, its function having been superseded by asynchronous response mode. UP is an exception to the usual rule in normal response mode that a secondary must receive the poll flag before transmitting; while a secondary ''must'' respond to any frame with the poll bit set, it ''may'' respond to a UP frame with the poll bit clear if it has data to transmit. If the lower-level communication channel is capable of avoiding collisions (as it is in loop mode), UP ''to the broadcast address'' allows multiple secondaries to respond without having to poll them individually.
The TEST U frame was not included in early HDLC standards, but was added later.

==== Loop mode ====
A special mode of SDLC operation which is supported by e.g. the [[Zilog SCC]] but was not incorporated into HDLC is SDLC loop mode.{{R|GA27-3093-3|p=42–49,58–59}} In this mode, a primary and a number of secondaries are connected in a unidirectional [[ring network]], with each one's output connected to the next's input. Each secondary is responsible for copying all frames which arrive at its input so that they reach the rest of the ring and eventually return to the primary. Except for this copying, a secondary operates in half-duplex mode; it only transmits when the protocol guarantees it will receive no input.

When a secondary is powered off, a [[relay]] connects its input directly to its output. When powering on, a secondary waits for an opportune moment and then goes "on-loop" inserting itself into the data stream with a one-bit delay. A similar opportunity is used to go "off-loop" as part of a clean shutdown.

In SDLC loop mode, frames arrive in a group, ending (after the final flag) with an all-ones idle signal. The first seven 1-bits of this (the pattern 01111111) constitute a "go-ahead" sequence (also called EOP, end of poll) giving a secondary permission to transmit. A secondary which wishes to transmit uses its 1-bit delay to convert the final 1 bit in this sequence to a 0 bit, making it a flag character, and then transmits its own frames. After its own final flag, it transmits an all-ones idle signal, which will serve as a go-ahead for the next station on the loop.

The group starts with commands from the primary, and each secondary appends its responses. When the primary receives the go-ahead idle sequence, it knows that the secondaries are finished and it may transmit more commands.

The beacon (BCN) response is designed to help locate breaks in the loop. A secondary which does not see any incoming traffic for a long time begins sending "beacon" response frames, telling the primary that the link between that secondary and its predecessor is broken.

Because the primary also receives a copy of the commands it sent, which are indistinguishable from responses, it appends a special "turnaround" frame at the end of its commands to separate them from the responses. Any unique sequence which will not be interpreted by the secondaries will do, but the conventional one is a single all-zero byte.{{R|GA27-3093-3|p=44}} This is a "runt frame" with an address of 0 (reserved, unused) and no control field or frame check sequence. (Secondaries capable of full-duplex operation also interpret this as a "shut-off sequence", forcing them to abort transmission.{{R|GA27-3093-3|p=45}})

== Notes ==
{{Reflist}}

==References==
*{{cite journal
|url=http://www.research.ibm.com/journal/sj/151/ibmsj1501C.pdf
|title=System Network Architecture: An Overview
|first=J. H. |last=McFadyen
|journal=IBM Systems Journal
|volume=15 |issue=1 |pages=4–23 |year=1976 |doi=10.1147/sj.151.0004}}
*{{cite book
|first=Wendell
|last=Odom
|title=CCNA INTRO Exam Certification Guide: CCNA Self-study
|publisher=Cisco Press
|location=Indianapolis, IN
|year=2004
|isbn=1-58720-094-5
|url=https://archive.org/details/ccnaintroexamcer00wend
}}
*{{cite book
|last1=Friend
|first1=George E.
|first2=John L |last2=Fike |first3=H. Charles |last3=Baker |first4=John C |last4=Bellamy
|title=Understanding Data Communications
|edition=2nd
|year=1988
|publisher=Howard W. Sams & Company
|location=Indianapolis
|isbn=0-672-27270-9 |ref={{sfnref|Friend|1988}} }}
*{{cite book
|last1=Pooch
|first1=Udo W.
|first2=William H |last2=Greene |first3=Gary G |last3=Moss
|title=Telecommunications and Networking
|publisher=Little, Brown and Company
|location=Boston
|year=1983
|isbn=0-316-71498-4 |ref={{sfnref|Pooch|1983}} }}
*{{cite book
|last=Hura
|first=Gurdeep S.
|author2=Mukesh Singhal
|title=Data and computer communications: networking and internetworking
|year=2001
|publisher=CRC Press
|location=Indianapolis
|isbn=0-8493-0928-X
|url=https://archive.org/details/datacomputercomm0000hura
}}
*{{cite book |title=ITS Cabinet Standard |version=v01.02.17b |date=November 16, 2006 |publisher=Institute of Transportation Engineers |location=Washington, DC |page=96 |ref={{sfnref|ITS|2006}} |url=https://www.ite.org/pub/?id=e26a4960-2354-d714-51e1-fcd483b751aa#page=104 |quote=All communication within the ATC controller unit shall be SDLC-compatible command-response protocol, support 0-bit stuffing, and operate at a data rate of 614.4 Kilobits per second.}}

== External links ==
*{{cite tech report |url=http://www.bitsavers.org/pdf/ibm/datacomm/GA27-3093-2_SDLC_General_Information_Mar79.pdf |title=IBM Synchronous Data Link Control: General Information |edition=3rd |date=March 1979 |id=Document No. GA27-3093-2 |author=IBM Communication Products Division}}
*[https://web.archive.org/web/20181229220922/http://docwiki.cisco.com/wiki/Synchronous_Data_Link_Control_and_Derivatives Cisco page on Synchronous Data Link Control and Derivatives]
*[http://www.bitbus.org Bitbus/fieldbus community site.]

[[Category:Computer network technology]]
[[Category:Systems Network Architecture]]
[[Category:Link protocols]]
[[Category:Telecommunication protocols]]

State machine

2026-05-03T12:41:51Z

RS-485: Imported from Wikipedia (overwrite)

#REDIRECT [[Finite-state machine]] {{R short}}

Software flow control

2026-05-03T12:41:48Z

RS-485: Imported from Wikipedia (overwrite)

{{Short description|Flow control method}}
{{Redirect-distinguish|Xon|Xon (character)|XON (company)}}
{{refimprove|date=March 2009}}

'''Software flow control''' is a method of [[flow control (data)|flow control]] used in computer [[data link]]s, especially [[RS-232|RS-232 serial]]. It uses special codes, transmitted [[in-band signaling|in-band]], over the primary communications channel. These codes are generally called '''XOFF''' and '''XON''' (from "transmit off" and "transmit on", respectively). Thus, "software flow control" is sometimes called "XON/XOFF flow control". This is in contrast to flow control via dedicated [[Out-of-band data|out-of-band]] signals — "[[Flow control (data)#Hardware flow control|hardware flow control]]" — such as [[RS-232 RTS/CTS]].

== Representation ==

For systems using the [[ASCII]] character code, XOFF is generally represented using a [[character (computing)|character]] or [[byte]] with decimal value 19; XON with value 17.

The ASCII standard does not reserve any [[control character]]s for use as XON/XOFF specifically. However, it does provide four generic "device control" characters (DC1 through DC4). The [[Teletype Model 33]] ASR adopted two of these, DC3 and DC1, for use as XOFF and XON, respectively. This usage was copied by others, and is now a [[de facto standard]]. The keyboard equivalents of {{key press|Ctrl|S}} for XOFF, and {{key press|Ctrl|Q}} for XON, also derive from this usage.

{| class="wikitable"
|+ XOFF/XON representations in ASCII
! Code
! Meaning
! [[ASCII]]
! [[Decimal|Dec]]
! [[Hexadecimal|Hex]]
! Keyboard
|-
| XOFF
| Pause transmission
| DC3
| 19
| 13
| {{key press|Ctrl|S}}
|-
| XON
| Resume transmission
| DC1
| 17
| 11
| {{key press|Ctrl|Q}}
|}

== Mechanism ==

When one end of a data link is unable to accept any more data (or approaching that point), it sends XOFF to the other end. The other end receives the XOFF code, and suspends [[transmission (telecommunications)|transmission]]. Once the first end is ready to accept data again, it sends XON, and the other end resumes transmission.

For example, one may imagine a [[computer]] sending data to a slow [[printer (computing)|printer]]. Since the computer is faster at sending data than the printer can print it, the printer falls behind and approaches a situation where it would be overwhelmed by the data. The printer reacts to this situation by sending XOFF to the computer, which temporarily stops sending data. When the printer is again ready to receive more data, it sends XON to the computer, which starts sending data again.

XOFF/XON can be employed in both directions, for example, two [[teleprinter]]s connected to each other.

== Comparison with hardware flow control ==

The principal advantage of software flow control is the reduction in the number of [[electrical conductor]]s between sender and receiver. Given a [[ground (electricity)|common ground]], only two signals are needed, one to send and the other to receive. Hardware flow control requires additional wires between the two devices. It also requires specific hardware implementation, which had more significant costs in earlier days of computing (i.e., 1960s and 70s).

However, software flow control is not without its problems. The most important drawback is that software flow control is less reliable. Sending XOFF requires at least one character time to transmit, and may be queued behind already-transmitted data still in buffers. Hardware signals may be asserted almost instantaneously, and out-of-order.

{| class="wikitable floatright"|
|+ Summary of flow control tradeoffs
! {{tooltip|2=Flow control method|Type}}
! {{tooltip|2=Prevents loss of data due to buffer overruns|Data integrity}}
! {{tooltip|2=Does not require additional wiring and electronics|Low cost}}
! {{tooltip|2=All bytes can be transmitted without using escape mechanisms|Out of Band}}
|-
| Hardware flow control
| Most reliable
| {{No}}
| {{Yes}}
|-
| On-chip software f.c.
| Good
| {{Some}}
| {{No}}
|-
| Software f.c. (FIFO disabled)
| Good, but slow
| {{Yes}}
| {{No}}
|-
| Software f.c. (FIFO enabled)
| Unreliable
| {{Yes}}
| {{No}}
|}

As the name "software flow control" implies, flow control using this method is ''usually'' implemented in software (or [[firmware]]), which can cause further delays in XOFF response. These delays can lead to data corruption due to [[buffer overruns]]. Hardware flow control, on the other hand, is typically under the direct control of the transmitting [[Universal asynchronous receiver/transmitter|UART]], which is able to cease transmission immediately, without the intervention of higher levels. To handle the latency caused by builtin [[FIFO (computing and electronics)|FIFOs]], more advanced UARTs, like the 16950, provide "on-chip" software flow control.<ref name="moxa">{{Cite book |last=Yang |first=Casper |url=https://moxa.com.cn/getmedia/2489d383-e47d-4258-94ba-9075fbeb618f/moxa-the-secrets-of-uart-fifo-tech-note-v1.0.pdf |title=The Secrets of Flow Control in Serial Communication |publisher=Moxa Technical Writing Center |year=2009 |edition=1.0 |series=Moxa Tech Note |publication-date=September 30, 2009 |language=EN |access-date=Aug 4, 2022 |archive-url=https://web.archive.org/web/20220804214055/https://moxa.com.cn/getmedia/2489d383-e47d-4258-94ba-9075fbeb618f/moxa-the-secrets-of-uart-fifo-tech-note-v1.0.pdf |archive-date=Aug 4, 2022}}</ref> UARTs that lack such support, like the [[16550 UART|16550]], may suffer from buffer overruns when using software flow control, although this can be somewhat mitigated by disabling the UART's FIFO.<ref name="moxa" />

Finally, since the XOFF/XON codes are sent in-band, they cannot appear in the data being transmitted without being mistaken for flow control commands. Any data containing the XOFF/XON codes thus must be encoded in some manner for proper transmission, with corresponding overhead. This is frequently done with some kind of [[escape sequence]]. For printing devices that directly interpret ASCII codes, this is not a large problem, because the XON and XOFF codes use [[ASCII]] "device control" code numbers.

== Applications ==

Software flow control is used extensively by low-speed devices, especially older [[printer (computing)|printer]]s and [[dumb terminal]]s, to indicate they are temporarily unable to accept more data. Typically, this is due to a combination of limited [[Output (computing)|output]] rate and any [[Data buffer|buffers]] being full. Some terminal control packages, such as [[termcap]], employ "padding" (short delays using millisecond granularity<ref>{{cite web|url=https://www.gnu.org/software/termutils/manual/termcap-1.3/html_node/termcap_10.html|title=The Termcap Library - Describe Padding|website=www.gnu.org}}</ref>) to allow such equipment sufficient time to perform the requested actions without the need to assert XOFF.

XOFF/XON are still sometimes used manually by computer operators, to pause and restart output which otherwise would [[scrolling|scroll]] off the display too quickly.

[[Terminal emulator]] software generally implements XOFF/XON support as a basic function. This generally includes the [[system console]] on modern [[Unix]] and [[Linux]] machines, as well as [[graphical user interface|GUI]] emulators such as [[xterm]] and the [[Win32 console]].

Robust XON is a technique to restart communication, just in case it was stopped by an accidentally received XOFF. The receiving unit sends periodic XON characters when it can receive data, and the line is idle. One common use is by serial printers (like [[HP LaserJet]] II) to indicate they are online and ready to receive data. The XON is sent every 1 to 30 seconds depending on the printer's firmware design.

==See also==
* [[Ethernet flow control]]

== References ==
{{Reflist}}
* {{cite web |url=http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=bpl06142&locale=en_US |title=HP LaserJet IIP and IIP Plus Printers - Control Panel Keys and Menus |publisher=[[Hewlett-Packard]] |archiveurl=https://web.archive.org/web/20060509012616/http://h20000.www2.hp.com/bizsupport/TechSupport/Document.jsp?objectID=bpl06142&locale=en_US |archivedate=May 9, 2006}}

[[Category:Flow control (data)]]

Software

2026-05-03T12:41:43Z

RS-485: Imported from Wikipedia (overwrite)

{{Short description|Instructions a computer can execute}}
{{Other uses}}
{{pp|small=yes}}
{{Use dmy dates|date=May 2017}}

[[File:JavaScript_code.png|thumb|Software written in the [[JavaScript]] language]]
'''Software''' consists of [[computer program]]s that instruct the [[Execution (computing)|execution]] of a [[computer]].<ref name="pis-p16">{{cite book
| last = Stair
| first = Ralph M.
| title = Principles of Information Systems, Sixth Edition
| publisher = Thomson
| year = 2003
| page = 16
| isbn = 0-619-06489-7
| quote = Software consists of computer programs that govern the operation of the computer.
}}</ref> Software also includes design documents and specifications.

The history of software is closely tied to the development of digital computers in the mid-20th century. Early programs were written in the [[machine language]] specific to the hardware. The introduction of [[high-level programming language]]s in 1958 allowed for more human-readable instructions, making [[software development]] easier and more portable across different [[computer architecture]]s. Software in a programming language is run through a [[compiler]] or [[Interpreter (computing)|interpreter]] to [[execution (computing)|execute]] on the architecture's hardware. Over time, software has become complex, owing to developments in [[Computer network|networking]], [[operating systems]], and [[databases]].

Software can generally be categorized into two main types:
# [[operating system]]s, which manage hardware resources and provide services for applications
# [[application software]], which performs specific tasks for users

The rise of [[cloud computing]] has introduced the new software delivery model [[software as a service]] (SaaS). In SaaS, applications are hosted by a [[application service provider|provider]] and [[HTTP|accessed]] over the [[Internet]].

The process of developing software involves several stages. The stages include [[software design]], [[Computer programming|programming]], [[software testing|testing]], [[software release life cycle|release]], and [[Software maintenance|maintenance]]. [[Software quality assurance]] and [[Information security|security]] are critical aspects of software development, as [[Computer bug|bugs]] and [[vulnerability (computing)|security vulnerabilities]] can lead to system failures and security breaches. Additionally, legal issues such as software licenses and intellectual property rights play a significant role in the distribution of software products.

==History==
{{Main|History of software}}
The first use of the word ''software'' to describe computer programs is credited to mathematician [[John Tukey|John Wilder Tukey]] in 1958.{{sfn|Jones|2014|pp=19, 22}}{{sfn|Tracy|2021|p=2}}<ref>{{cite encyclopedia |author= |date=2024 |title=software (n.), sense 2.a |url=https://doi.org/10.1093/OED/3803978366 |encyclopedia=Oxford English dictionary |location= |publisher=Oxford University Press |doi=10.1093/OED/3803978366 |access-date=2025-07-15}}</ref> The first programmable computers, which appeared at the end of the 1940s,{{sfn|Gabbrielli|Martini|2023|p=519}} were programmed in [[machine language]]. Machine language is difficult to debug and not [[portability (computing)|portable]] across different computers.{{sfn|Gabbrielli|Martini|2023|pp=520–521}} Initially, hardware resources were more expensive than [[human resources]].{{sfn|Gabbrielli|Martini|2023|p=522}} As programs became complex, [[programmer productivity]] became the bottleneck. The introduction of [[high-level programming language]]s in 1958 [[abstraction (computing)|hid]] the details of the hardware and expressed the underlying [[algorithm]]s into the code.{{sfn|Gabbrielli|Martini|2023|p=521}}{{sfn|Tracy|2021|p=1}} Early languages include [[Fortran]], [[Lisp (programming language)|Lisp]], and [[COBOL]].{{sfn|Tracy|2021|p=1}}

==Types==
{{See also|Software categories}}

[[File:Operating system placement (software).svg|thumb|upright|A diagram showing how the [[User (computing)|user]] interacts with [[application software]] on a typical [[desktop computer]]. The application software layer interfaces with the [[operating system]], which in turn communicates with the [[computer hardware|hardware]]. The arrows indicate information flow.]]
There are two main types of software:
* [[Operating system]]s are "the [[abstraction layer|layer of software]] that manages a computer's resources for its users and their [[Application software|application]]s".{{sfn|Anderson|Dahlin|2014|p=6}} There are three main purposes that an operating system fulfills:{{sfn|Anderson|Dahlin|2014|p=7}}
**Allocating resources between different applications, deciding when they will receive [[central processing unit]] (CPU) time or space in [[computer memory|memory]].{{sfn|Anderson|Dahlin|2014|p=7}}
**Providing an interface that abstracts the details of accessing [[Computer hardware|hardware]] details (like physical memory) to make things easier for programmers.{{sfn|Anderson|Dahlin|2014|p=7}}{{sfn|Tanenbaum|Bos|2023|p=5}}
**Offering common services, such as an interface for accessing network and disk devices. This enables an application to be run on different hardware without needing to be rewritten.{{sfn|Anderson|Dahlin|2014|pp=7, 9, 13}}
* [[Application software]] runs on top of the operating system and uses the computer's resources to perform a task.{{sfn|Anderson|Dahlin|2014|pp=6-7}} There are many different types of application software because the range of tasks that can be performed with modern computers is so large.{{sfn|Jones|2014|p=121}} Applications account for most software{{sfn|Tracy|2021|p=66}} and require the [[Operating environment|environment]] provided by an operating system, and often other applications, in order to function.{{sfn|Tracy|2021|p=72}}

[[File:Locale_RS6_Comparison of on-premise, IaaS, PaaS, and SaaS.png|thumb|Comparison of on-premise hardware and software, [[infrastructure as a service]] (IaaS), [[platform as a service]] (PaaS), and [[software as a service]] (SaaS)|upright=2.4|center]]
Software can also be categorized by how it is [[software deployment|deployed]]. Traditional applications are purchased with a perpetual [[software license|license]] for a specific version of the software, downloaded, and run on hardware belonging to the purchaser.{{sfn|O'Regan|2022|p=386}} The rise of [[the Internet]] and [[cloud computing]] enabled a new model, [[software as a service]] (SaaS),{{sfn|Campbell-Kelly|Garcia-Swartz|2015|pp=156-157}} in which the provider hosts the software (usually built on top of rented [[infrastructure as a service|infrastructure]] or [[platform as a service|platform]]s){{sfn|Rosati |Lynn|2020|p=23}} and provides the use of the software to customers, often in exchange for a [[subscription fee]].{{sfn|O'Regan|2022|p=386}} By 2023, SaaS products—which are usually delivered via a [[web application]]—had become the primary method that companies deliver applications.{{sfn|Watt|2023|p=4}}

==Software development and maintenance==
[[File:Locale_RS6_Traditional software development life cycle diagram.png|thumb|upright=2.5|center|Diagram for a traditional [[software development life cycle]] from 1988. The numbers represent the typical cost of each phase.]]

Software companies aim to deliver a high-quality product on time and under budget. A challenge is that [[software development effort estimation]] is often inaccurate.{{sfn|O'Regan|2022|p=7}} [[Software development]] begins by conceiving the project, evaluating its feasibility, analyzing the business requirements, and making a [[software design]].{{sfn|O'Regan|2022|p=5}}{{sfn|Dooley|2017|p=1}} Most software projects speed up their development by [[software reuse|reusing]] or incorporating existing software, either in the form of [[commercial off-the-shelf]] (COTS) or [[open-source software]].{{sfn|O'Regan|2022|pp=18, 110-111}}{{sfn|Tracy|2021|pp=43, 76}} [[Software quality assurance]] is typically a combination of manual [[code review]] by other engineers{{sfn|O'Regan|2022|pp=117-118}} and automated [[software testing]]. Due to time constraints, testing cannot cover all aspects of the software's intended functionality, so developers often focus on the most critical functionality.{{sfn|O'Regan|2022|p=54}} [[Formal method]]s are used in some safety-critical systems to prove the correctness of code,{{sfn|O'Regan|2022|p=267}} while [[user acceptance testing]] helps to ensure that the product meets customer expectations.{{sfn|O'Regan|2022|p=20}} There are a variety of [[software development methodologies]], which vary from completing all steps in order to concurrent and iterative models.{{sfn|O'Regan|2022|p=9}} Software development is driven by [[software requirements|requirements]] taken from prospective users, as opposed to maintenance, which is driven by events such as a change request.{{sfn|Tripathy |Naik|2014|p=26}}

Frequently, software is [[software release life cycle|released]] in an incomplete state when the development team runs out of time or funding.{{sfn |Reifer|2012|p=22}} Despite [[software testing|testing]] and [[Software quality assurance|quality assurance]], virtually all software contains [[software bug|bugs]] where the system does not work as intended. Post-release [[software maintenance]] is necessary to remediate these bugs when they are found and keep the software working as the environment changes over time.{{sfn|Tripathy |Naik|2014|pp=4, 27}} New features are often added after the release. Over time, the level of maintenance becomes increasingly restricted before being cut off entirely when the product is withdrawn from the market.{{sfn|Tripathy |Naik|2014|p=89}} As software [[software aging|ages]], it becomes known as [[legacy software]] and can remain in use for decades, even if there is no one left who knows how to fix it.{{sfn|Tracy|2021|p=3}} Over the lifetime of the product, software maintenance is estimated to comprise 75 percent or more of the total development cost.{{sfn|Varga|2018|p=6}}{{sfn|Ulziit ''et al.''|2015|p=764}}

Completing a software project involves various forms of expertise, not just in [[software programmer]]s but also testing, documentation writing, [[Software project management|project management]], [[graphic design]], [[user experience]], user support, [[marketing]], and fundraising.{{sfn|Tucker |Morelli |de Silva |2011|p=7}}{{sfn|Stull|2018|pp=24-25}}{{sfn|Dooley|2017|p=1}}

==Quality and security==
{{main article|Software quality|Computer security}}
[[Software quality]] is defined as meeting the stated requirements as well as customer expectations.{{sfn|Galin|2018|p=3}} Quality is an overarching term that can refer to a code's correct and efficient behavior, its reusability and [[porting|portability]], or the ease of modification.{{sfn|Galin|2018|p=26}} It is usually more cost-effective to build quality into the product from the beginning rather than try to add it later in the development process.{{sfn|O'Regan|2022|pp=68, 117}} Higher quality code will reduce lifetime cost to both suppliers and customers as it is more reliable and [[maintainability|easier to maintain]].{{sfn|O'Regan|2022|pp=3, 268}}{{sfn|Varga|2018|p=12}} Software failures in [[safety-critical system]]s may result in serious harm, including injury or death.{{sfn|O'Regan|2022|pp=3, 268}} By some estimates, the cost of poor quality software can be as high as 20 to 40 percent of sales.{{sfn|O'Regan|2022|p=119}} Despite developers' goal of delivering a product that works entirely as intended, virtually all software contains bugs.{{sfn|Ablon|Bogart|2017|p=1}}

The rise of the Internet also greatly increased the need for [[computer security]] as it enabled malicious actors to conduct [[cyberattack]]s remotely.{{sfn|Campbell-Kelly|Garcia-Swartz|2015|p=164}}{{sfn|O'Regan|2022|p=266}} If a bug creates a security risk, it is called a [[vulnerability (computing)|vulnerability]].{{sfn|Ablon|Bogart|2017|p=2}}{{sfn|Daswani |Elbayadi|2021|p=25}} [[Software patch]]es are often released to fix identified vulnerabilities, but those that remain unknown ([[Zero-day (computing)|zero day]]s) as well as those that have not been patched are still liable for exploitation.{{sfn|Daswani |Elbayadi|2021|pp=26-27}} Vulnerabilities vary in their ability to be [[Exploit (computer security)|exploit]]ed by malicious actors,{{sfn|Ablon|Bogart|2017|p=2}} and the actual risk is dependent on the nature of the vulnerability as well as the value of the surrounding system.{{sfn|Haber |Hibbert|2018|pp=5-6}} Although some vulnerabilities can only be used for [[denial of service]] attacks that compromise a system's availability, others allow the attacker to [[code injection|inject]] and run their own code (called [[malware]]), without the user being aware of it.{{sfn|Ablon|Bogart|2017|p=2}} To thwart cyberattacks, all software in the system must be designed to withstand and recover from external attack.{{sfn|O'Regan|2022|p=266}} Despite efforts to ensure security, a significant fraction of computers are infected with malware.{{sfn|Kitchin |Dodge|2011|p=37}}

==Encoding and execution==

===Programming languages===
{{main|Programming language}}
[[File:Locale_RS6_C Hello World Program.png|thumb|right|upright=1.3|The [[source code]] for a computer program in [[C (programming language)|C]]. The gray lines are [[comment (computer programming)|comments]] that explain the program to humans. When [[compiled]] and [[Execution (computing)|run]], it will output "[["Hello, World!" program|Hello, world!]]".]]
Programming languages are the format in which software is written. Since the 1950s, thousands of different programming languages have been invented; some have been in use for decades, while others have fallen into disuse.{{sfn|Tracy|2021|p=117}} Some definitions classify [[machine code]]—the exact instructions directly implemented by the hardware—and [[assembly language]]—a more human-readable alternative to machine code whose statements can be translated one-to-one into machine code—as programming languages.{{sfn|Tracy|2021|pp=118–120}} Programs written in the [[high-level programming languages]] used to create software share a few main characteristics: knowledge of machine code is not necessary to write them, they can be [[ported]] to other computer systems, and they are more concise and human-readable than machine code.{{sfn|Tracy|2021|pp=118–119}} They must be both human-readable and capable of being translated into unambiguous instructions for computer hardware.{{sfn|Kitchin |Dodge|2011|p=26}}

===Compilation, interpretation, and execution===

The invention of high-level programming languages was simultaneous with the [[compiler]]s needed to translate them automatically into machine code.{{sfn|Tracy|2021|p=121}} Most programs do not contain all the resources needed to run them and rely on external [[software library|libraries]]. Part of the compiler's function is to link these files in such a way that the program can be executed by the hardware. Once compiled, the program can be saved as an [[object file]] and the [[Loader (computing)|loader]] (part of the operating system) can take this saved file and [[execution (computing)|execute]] it as a [[process]] on the computer hardware.{{sfn|Tracy|2021|pp=122-123}} Some programming languages use an [[Interpreter (computing)|interpreter]] instead of a compiler. An interpreter converts the program into machine code at [[execution (computing)|run time]], which makes them 10 to 100 times slower than compiled programming languages.{{sfn|O'Regan|2022|p=375}}{{sfn|Sebesta|2012|p=28}}

==Legal issues==
===Liability===
{{main article|Software product liability}}
Software is often released with the knowledge that it is incomplete or contains bugs.{{cn|reason=see Talk:Software#Legal_issues_assertions|date=June 2025}} Purchasers knowingly buy it in this state,{{cn|reason=see Talk:Software#Legal_issues_assertions|date=June 2025}} which has led to a legal regime where [[Product liability|liability]] for software products is significantly curtailed compared to other products.{{sfn|Kitchin |Dodge|2011|pp=36-37}}

===Licenses===
{{Main|Software license|Software copyright}}
[[File:Locale_RS6_Cube in Blender Editor.jpg|thumb|[[Blender (software)|Blender]], a [[free software]] program]]
Since the mid-1970s, software and its source code have been protected by [[copyright law]] that vests the owner with the exclusive right to copy the code. The underlying ideas or algorithms are not protected by copyright law, but are sometimes treated as a [[trade secret]] and concealed by such methods as [[non-disclosure agreement]]s.{{sfn|O'Regan|2022|pp=394-396}} A [[software copyright]] is often owned by the person or company that financed or made the software (depending on their contracts with employees or [[Independent contracting in the United States|contractor]]s who helped to write it).{{sfn|O'Regan|2022|p=403}} Some software is in the [[public domain]] and has no restrictions on who can use it, copy or share it, or modify it; a notable example is software written by the [[Federal government of the United States|United States Government]].{{cn|reason=see Talk:Software#Legal_issues_assertions|date=June 2025}} [[Free and open-source software]] also allow free use, sharing, and modification, perhaps with a few specified conditions.{{sfn|O'Regan|2022|p=403}} The use of some software is governed by an agreement ([[software license]]) written by the copyright holder and imposed on the user. [[Proprietary software]] is usually sold under a restrictive license that limits its use and sharing.{{sfn|O'Regan|2022|pp=394, 404}} Some free software licenses require that modified versions must be released under the same license, which prevents the software from being sold
or distributed under proprietary restrictions.{{sfn|Langer|2016|pp=44-45}}

===Patents===
{{Main|Software patent|Software patent debate}}
[[Patent]]s give an inventor an exclusive, time-limited license for a novel product or process.{{sfn|O'Regan|2022|p=395}} Ideas about what software could accomplish are not protected by law and concrete implementations are instead covered by [[copyright law]]. In some countries, a requirement for the claimed invention to have an effect on the physical world may also be part of the requirements for a software patent to be held valid.<ref>Gerardo Con Díaz, "The Text in the Machine: American Copyright Law and the Many Natures of Software, 1974–1978", ''Technology and Culture'' 57 (October 2016), 753–79.</ref> [[Software patent]]s have been [[Software patent debate|historically controversial]]. Before the 1998 case ''[[State Street Bank & Trust Co. v. Signature Financial Group, Inc.]]'', software patents were generally not recognized in the United States. In that case, the [[Supreme Court of the United States|Supreme Court]] decided that business processes could be patented.{{sfn|Jones|2014|p=19}} Patent applications are complex and costly, and lawsuits involving patents can drive up the cost of products.{{sfn|O'Regan|2022|p=398}} Unlike copyrights, patents generally only apply in the jurisdiction where they were issued.{{sfn|O'Regan|2022|p=399}}

==Impact==
{{further |Information Age}}

[[File:Locale_RS6_A computer graphic of the Queen Elizabeth carrier and carrier group.jpg|thumb|Computer-generated simulations are one of the advances enabled by software.{{sfn|Manovich|2013|p=333}}]]
Engineer [[Capers Jones]] writes that "computers and software are making profound changes to every aspect of human life: education, work, warfare, entertainment, medicine, law, and everything else".{{sfn|Jones|2014|p=32}} It has become ubiquitous in [[everyday life]] in [[developed countries]].{{sfn|Kitchin |Dodge|2011|p=iv}} In many cases, software augments the functionality of existing technologies such as household [[Home appliance|appliances]] and [[elevator]]s.{{sfn|Kitchin |Dodge|2011|p=5}} Software also spawned entirely new technologies such as [[the Internet]], [[video games]], [[mobile phones]], and [[GPS]].{{sfn|Kitchin |Dodge|2011|p=5}}{{sfn|Jones|2014|p=xxviii}} New methods of communication, including [[email]], [[Internet forum|forum]]s, [[blog]]s, [[microblogging]], [[wiki]]s, and [[social media]], were enabled by the Internet.{{sfn|Manovich|2013|p=329}} Massive amounts of knowledge exceeding any paper-based library are now available with a quick [[web search]].{{sfn|Jones|2014|p=xxviii}} Most creative professionals have switched to software-based tools such as [[computer-aided design]], [[3D modeling]], digital [[image editing]], and [[computer animation]].{{sfn|Manovich|2013|p=333}} Almost every complex device is controlled by software.{{sfn|Jones|2014|p=xxviii}}

==References==
{{reflist}}

===Sources===
{{refbegin|indent=yes}}
*{{cite book |last1=Ablon |first1=Lillian |last2=Bogart |first2=Andy |title=Zero Days, Thousands of Nights: The Life and Times of Zero-Day Vulnerabilities and Their Exploits |date=2017 |publisher=Rand Corporation |isbn=978-0-8330-9761-3 |language=en|url=https://www.rand.org/content/dam/rand/pubs/research_reports/RR1700/RR1751/RAND_RR1751.pdf}}
*{{cite book |last1=Anderson |first1=Thomas |last2=Dahlin |first2=Michael |author1-link=Thomas E. Anderson |title=Operating Systems: Principles and Practice |date=2014 |publisher=Recursive Books |isbn=978-0-9856735-2-9 |edition=2 |language=en}}
*{{cite book |last1=Campbell-Kelly |first1=Martin |last2=Garcia-Swartz |first2=Daniel D. |title=From Mainframes to Smartphones: A History of the International Computer Industry |date=2015 |publisher=Harvard University Press |isbn=978-0-674-28655-9 |language=en}}
*{{cite book |last1=Daswani |first1=Neil|authorlink=Neil Daswani |last2=Elbayadi |first2=Moudy |title=Big Breaches: Cybersecurity Lessons for Everyone |date=2021 |publisher=Apress |isbn=978-1-4842-6654-0}}
*{{Cite book |last=Dooley |first=John F. |title=Software Development, Design and Coding: With Patterns, Debugging, Unit Testing, and Refactoring |date=2017 |publisher=Apress |isbn=978-1-4842-3153-1 |language=en}}
*{{cite book |last1=Gabbrielli |first1=Maurizio |last2=Martini |first2=Simone |title=Programming Languages: Principles and Paradigms |date=2023 |publisher=Springer |isbn=978-3-031-34144-1 |language=en|edition=2nd}}
*{{cite book |last1=Galin |first1=Daniel |title=Software Quality: Concepts and Practice |date=2018 |publisher=John Wiley & Sons |isbn=978-1-119-13449-7 |language=en}}
*{{cite book |last1=Haber |first1=Morey J. |last2=Hibbert |first2=Brad |title=Asset Attack Vectors: Building Effective Vulnerability Management Strategies to Protect Organizations |date=2018 |publisher=Apress |isbn=978-1-4842-3627-7 |language=en}}
*{{cite book |last1=Jones |first1=Capers |title=The Technical and Social History of Software Engineering |date=2014 |publisher=Pearson Education |isbn=978-0-321-90342-6 |language=en}}
*{{cite book |last1=Kitchin |first1=Rob |last2=Dodge |first2=Martin |title=Code/space: Software and Everyday Life |date=2011 |publisher=MIT Press |isbn=978-0-262-04248-2 |language=en}}
*{{Cite book |last=Langer |first=Arthur M. |title=Guide to Software Development: Designing and Managing the Life Cycle |date=2016 |publisher=Springer |isbn=978-1-4471-6799-0 |language=en}}
*{{cite book |last1=Manovich |first1=Lev |title=Software Takes Command |date=2013 |publisher=Bloomsbury Academic |isbn=978-1-62356-745-3 |language=en}}
*{{cite book |last1=O'Regan |first1=Gerard |title=Concise Guide to Software Engineering: From Fundamentals to Application Methods |date=2022 |publisher=Springer Nature |isbn=978-3-031-07816-3 |language=en}}
*{{cite book |last1=Osterweil |first1=Leon J. |title=Perspectives on the Future of Software Engineering: Essays in Honor of Dieter Rombach |date=2013 |publisher=Springer |isbn=978-3-642-37395-4 |pages=237–254 |language=en |chapter=What Is Software? The Role of Empirical Methods in Answering the Question}}
*{{cite journal |last1=Rahman |first1=Hanif Ur |last2=da Silva |first2=Alberto Rodrigues |last3=Alzayed |first3=Asaad |last4=Raza |first4=Mushtaq |title=A Systematic Literature Review on Software Maintenance Offshoring Decisions |journal=Information and Software Technology |date=2024 |volume=172 |article-number=107475 |doi=10.1016/j.infsof.2024.107475|ref={{sfnref|Rahman et al.|2024}}}}
*{{cite book |last1=Reifer |first1=Donald J. |title=Software Maintenance Success Recipes |date=2012 |publisher=CRC Press |isbn=978-1-4398-5167-8 |language=en}}
*{{cite book |last1=Rosati |first1=Pierangelo |last2=Lynn |first2=Theo |title=Measuring the Business Value of Cloud Computing |date=2020 |publisher=Springer International Publishing |isbn=978-3-030-43198-3 |pages=19–37 |language=en |chapter=Measuring the Business Value of Infrastructure Migration to the Cloud}}
* {{cite book |last1=Sebesta |first1=Robert W. |title=Concepts of Programming Languages |date=2012 |publisher=Addison-Wesley |isbn=978-0-13-139531-2 |edition=10 |language=en}}
*{{cite book |last1=Stull |first1=Edward |title=UX Fundamentals for Non-UX Professionals: User Experience Principles for Managers, Writers, Designers, and Developers |date=2018 |publisher=Apress |isbn=978-1-4842-3811-0 |language=en}}
*{{cite book |last1=Tanenbaum |first1=Andrew S.|authorlink=Andrew S. Tanenbaum |last2=Bos |first2=Herbert |title=Modern Operating Systems, Global Edition |date=2023 |publisher=Pearson Higher Ed |isbn=978-1-292-72789-9 |language=en}}
*{{cite book |last1=Tracy |first1=Kim W. |title=Software: A Technical History |date=2021 |publisher=Morgan & Claypool Publishers |isbn=978-1-4503-8724-8 |language=en}}
*{{cite book |last1=Tripathy |first1=Priyadarshi |last2=Naik |first2=Kshirasagar |title=Software Evolution and Maintenance: A Practitioner's Approach |date=2014 |publisher=John Wiley & Sons |isbn=978-0-470-60341-3 |language=en}}
*{{Cite book |last1=Tucker |first1=Allen |title=Software Development: An Open Source Approach |last2=Morelli |first2=Ralph |last3=de Silva |first3=Chamindra |date=2011 |publisher=CRC Press |isbn=978-1-4398-8460-7 |language=en}}
*{{cite journal |last1=Ulziit |first1=Bayarbuyan |last2=Warraich |first2=Zeeshan Akhtar |last3=Gencel |first3=Cigdem |last4=Petersen |first4=Kai |title=A conceptual framework of challenges and solutions for managing global software maintenance |journal=Journal of Software: Evolution and Process |date=2015 |volume=27 |issue=10 |pages=763–792 |doi=10.1002/smr.1720|ref={{sfnref|Ulziit et al.|2015}}}}
*{{cite book |last1=Watt |first1=Andy |title=Building Modern SaaS Applications with C# And . NET: Build, Deploy, and Maintain Professional SaaS Applications |date=2023 |publisher=Packt |isbn=978-1-80461-087-9 |language=en}}
*{{cite book |last1=Varga |first1=Ervin |title=Unraveling Software Maintenance and Evolution: Thinking Outside the Box |date=2018 |publisher=Springer |isbn=978-3-319-71303-8 |language=en}}
{{refend}}

{{Software digital distribution platforms|state=collapsed}}
{{subject bar|Free and open-source software|auto=1}}
{{Authority control}}

[[Category:Software| ]]

File:Locale RS6 Traditional software development life cycle diagram.png

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RS-485: Imported from Wikipedia

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RS-485: Imported from Wikipedia

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File:Locale RS6 Cube in Blender Editor.jpg

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RS-485: Imported from Wikipedia

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File:Locale RS6 Comparison of on-premise, IaaS, PaaS, and SaaS.png

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RS-485: Imported from Wikipedia

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RS-485: Imported from Wikipedia

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File:Locale RS6 A computer graphic of the Queen Elizabeth carrier and carrier group.jpg

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RS-485: Imported from Wikipedia

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Smart card

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RS-485: Imported from Wikipedia (overwrite)

{{Short description|Pocket-sized card with authentication circuitry}}
{{Use dmy dates|date=May 2022}}
{{Redirect|IC card|Japanese transportation IC cards ([[Suica]], [[PASMO]], etc.)|Nationwide Mutual Usage Service}}
[[File:Locale_RS6_New Finnish ID card (front side).jpg|thumb| [[Finnish identity card|Finnish national identity card]]]]
A '''smart card''' ('''SC'''), '''chip card''', or '''integrated circuit card''' ('''ICC''' or '''IC card'''), is a card used to control access to a resource. It is typically a plastic credit card-sized card with an [[Embedded system|embedded]] [[integrated circuit]] (IC) chip.<ref>{{Cite web |title=ISO/IEC 7816-2:2007 – Assignment of contacts C4 and C8 |url=http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=45989 |website=iso.org |access-date=20 August 2015 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304093036/http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=45989 |url-status=live }}</ref> Many smart cards include a pattern of metal contacts to electrically connect to the internal chip. Others are [[Contactless smart card|contactless]], and some are both. Smart cards can provide personal identification, authentication, data storage, and application processing.<ref>{{ cite book |title=Multi-application Smart Cards |publisher=Cambridge University Press }}</ref> Applications include identification, financial, public transit, computer security, schools, and healthcare. Smart cards may provide strong security authentication for [[single sign-on]] (SSO) within organizations. Numerous nations have deployed smart cards throughout their populations.

The [[universal integrated circuit card]] (UICC) for mobile phones, installed as pluggable [[SIM card]] or embedded [[eSIM]], is also a type of smart card. {{As of|2015}}, 10.5{{nbsp}}billion smart card IC chips are manufactured annually, including 5.44{{nbsp}}billion SIM card IC chips.<ref name="ihs">{{cite news |last1=Tait |first1=Don |title=Smart card IC shipments to reach 12.8 billion units in 2020 |url=https://technology.ihs.com/582859/smart-card-ic-shipments-to-reach-128-billion-units-in-2020 |access-date=24 October 2019 |work=IHS Technology |publisher=IHS Markit |date=25 August 2016 |archive-date=24 October 2019 |archive-url=https://web.archive.org/web/20191024214524/https://technology.ihs.com/582859/smart-card-ic-shipments-to-reach-128-billion-units-in-2020 |url-status=live }}</ref>

== History ==
{{See also|Payment card}}

The basis for the smart card is the [[silicon]] [[integrated circuit]] (IC) chip.<ref name="Chen">{{cite book |last1=Chen |first1=Zhiqun |title=Java Card Technology for Smart Cards: Architecture and Programmer's Guide |date=2000 |publisher=[[Addison-Wesley Professional]] |isbn=9780201703290 |pages=[https://archive.org/details/javacardtmtechno00zhiq/page/3 3]–4 |url=https://archive.org/details/javacardtmtechno00zhiq |url-access=registration }}</ref> It was invented by [[Robert Noyce]] at [[Fairchild Semiconductor]] in 1959. The invention of the silicon integrated circuit led to the idea of incorporating it onto a plastic card in the late 1960s.<ref name="Chen"/>

=== Invention ===
[[File:Locale_RS6_Prototype moreno2.jpg|thumb|One of the first smart card prototypes, created by its inventor [[Roland Moreno]] around 1975. The chip has not yet been miniaturized. On this prototype, one can see how each pin of the microchip (center) is connected to the exterior world by a copper connector.]]
[[File:Locale_RS6_1979 erste G&D-Chipkarte (8 Kontakte).jpg|thumb|First smart card manufactured by [[Giesecke+Devrient|Giesecke & Devrient]] in 1979, already with the finally standardized dimension (ID-1) and a contact area with eight pads (initially on the upper left corner)]]

The idea of incorporating an [[integrated circuit]] chip onto a plastic card was first introduced by the German engineer [[Helmut Gröttrup]]. In February 1967, Gröttrup filed the patents DE1574074<ref>{{Cite patent |title=Nachahmungssicherer Identifizierungsschalter |country=DE |number=1574074 |status=application |pubdate=1971-11-25 |invent1=Gröttrup |inventor1-first=Helmut |fdate=1967-02-06 |inventorlink=Helmut Gröttrup }}</ref> and DE1574075<ref>{{Cite patent |title=Identifizierungsschalter mit induktiver Zuordnung |country=DE |number=1574075 |status=application |pubdate=1971-11-25 |invent1=Gröttrup |inventor1-first=Helmut |fdate=1967-02-06 |inventorlink=Helmut Gröttrup }}</ref> in West Germany for a tamper-proof identification switch based on a [[semiconductor device]] and described contactless communication via inductive coupling.<ref>{{Cite web |url=https://www.dpma.de/docs/postergalerieneu/34_chipkarte.pdf |title=Chipkarte Helmut Gröttrup "Identifizierungsschalter" |date=2021 |access-date=2023-03-31 |website=[[German Patent and Trade Mark Office]] |language=de |trans-title=Helmut Gröttrup "Identification Switch" |archive-date=7 April 2023 |archive-url=https://web.archive.org/web/20230407025611/https://www.dpma.de/docs/postergalerieneu/34_chipkarte.pdf |url-status=live }}</ref> Its primary use was intended to provide individual copy-protected keys for releasing the tapping process at unmanned gas stations. In September 1968, Gröttrup, together with [[Jürgen Dethloff]] as an investor, filed further patents for this identification switch, first in Austria<ref>{{Cite patent |title=Identifizierungsschalter |country=AT |number=287366 |status=patent |gdate=1971-01-21 |invent1=Dethloff |inventor1-first=Jürgen |fdate=1968-09-13 |pridate=1968-09-13 |invent2=Gröttrup |inventor2-first=Helmut |inventorlink=Jürgen Dethloff |inventorlink2=Helmut Gröttrup |assign1=Intelectron Patentverwaltung }}</ref> and in 1969 as subsequent applications in the United States,<ref>{{Cite patent |title=Identification System |country=US |number=3641316 |status=patent |gdate=1972-02-08 |invent1=Dethloff |inventor1-first=Jürgen |fdate=1970-08-17 |pridate=1969-06-30 |invent2=Gröttrup |inventor2-first=Helmut |inventorlink=Jürgen Dethloff |inventorlink2=Helmut Gröttrup }}</ref><ref>{{Cite patent |title=Identification Switch |country=US |number=3678250 |status=patent |gdate=1972-07-18 |invent1=Dethloff |inventor1-first=Jürgen |fdate=1969-09-15 |pridate=1968-09-13 |invent2=Gröttrup |inventor2-first=Helmut |inventorlink=Jürgen Dethloff |inventorlink2=Helmut Gröttrup }}</ref> Great Britain, West Germany and other countries.<ref>{{Cite book |title=From Eurocheque Card to Mobile Security 1968–2012 |last1=Böttge |first1=Horst |publisher=Battenberg Gietl Verlag |year=2013 |isbn=978-3866465497 |last2=Mahl |first2=Tobias |last3=Kamp |first3=Michael |editor-last=[[Giesecke+Devrient]] }}</ref>

Independently, Kunitaka Arimura of the Arimura Technology Institute in Japan developed a similar idea of incorporating an integrated circuit onto a plastic card, and filed a smart card patent in March 1970.<ref name="Chen"/><ref name="Jurgensen">{{cite book |last1=Jurgensen |first1=Timothy M. |last2=Guthery |first2=Scott B. |title=Smart Cards: The Developer's Toolkit |date=2002 |publisher=[[Prentice Hall Professional]] |isbn=9780130937308 |pages=2–3 |url=https://books.google.com/books?id=TyniOOmvzKEC&pg=PA2 |access-date=30 September 2019 |archive-date=19 August 2020 |archive-url=https://web.archive.org/web/20200819234226/https://books.google.com/books?id=TyniOOmvzKEC&pg=PA2 |url-status=live }}</ref> The following year, Paul Castrucci of [[IBM]] filed an American patent titled "Information Card" in May 1971.<ref name="Jurgensen"/>

In 1974 [[Roland Moreno]] patented a secured memory card later dubbed the "smart card".<ref name=cwhrmoreno>{{cite web |title=Monticello Memoirs Program |url=http://www.cwhonors.org/Search/his_8.asp |publisher=Computerworld honors |access-date=13 February 2012 |url-status=dead |archive-url=https://web.archive.org/web/20160303193616/http://www.cwhonors.org/Search/his_8.asp |archive-date=3 March 2016 }}</ref><ref>{{Cite web |url=http://www.cardwerk.com/smartcards/smartcard_history.aspx |title=history of smartcard invention |access-date=29 July 2016 |archive-date=25 April 2013 |archive-url=https://web.archive.org/web/20130425054528/http://www.cardwerk.com/smartcards/smartcard_history.aspx |url-status=dead }}</ref> In 1976, Jürgen Dethloff introduced the known element (called "the secret") to identify gate user as of USP 4105156.<ref>{{cite web |url=http://worldwide.espacenet.com/publicationDetails/originalDocument?FT=D&date=19780808&DB=EPODOC&locale=en_EP&CC=US&NR=4105156A&KC=A&ND=4 |title=Espacenet – Original document |publisher=Worldwide.espacenet.com |date=8 August 1978 |access-date=13 February 2014 |archive-date=12 March 2017 |archive-url=https://web.archive.org/web/20170312030034/https://worldwide.espacenet.com/publicationDetails/originalDocument?FT=D&date=19780808&DB=EPODOC&locale=en_EP&CC=US&NR=4105156A&KC=A&ND=4 |url-status=live }}</ref>

In 1977, Michel Ugon from [[Groupe Bull|Honeywell Bull]] invented the first [[microprocessor]] smart card with two [[integrated circuit|chips]]: one microprocessor and one [[computer memory|memory]], and in 1978, he patented the self-programmable one-chip microcomputer (SPOM) that defines the necessary architecture to program the chip. Three years later, [[Motorola]] used this patent in its "CP8". At that time, Bull had 1,200 patents related to smart cards. In 2001, Bull sold its CP8 division together with its patents to [[Schlumberger]], who subsequently combined its own internal smart card department and CP8 to create [[Axalto]]. In 2006, Axalto and Gemplus, at the time the world's top two smart-card manufacturers, merged and became [[Gemalto]]. In 2008, Dexa Systems spun off from Schlumberger and acquired Enterprise Security Services business, which included the smart-card solutions division responsible for deploying the first large-scale smart-card management systems based on [[public key infrastructure]] (PKI).

The first mass use of the cards was as a [[telephone card]] for payment in French [[payphone]]s, starting in 1983.<ref>{{Cite web |title=What is smart card? - Definition from WhatIs.com |url=https://www.techtarget.com/searchsecurity/definition/smart-card |access-date=2022-05-31 |website=SearchSecurity |language=en |archive-date=31 May 2022 |archive-url=https://web.archive.org/web/20220531110231/https://www.techtarget.com/searchsecurity/definition/smart-card |url-status=live }}</ref>

=== Carte bleue ===
After the Télécarte, microchips were integrated into all French ''[[Carte Bleue]]'' [[debit card]]s in 1992. Customers inserted the card into the merchant's [[point-of-sale]] (POS) terminal, then typed the [[personal identification number]] (PIN), before the transaction was accepted. Only very limited transactions (such as paying small [[Electronic toll collection|highway tolls]]) are processed without a PIN.

Smart-card-based "[[Stored value card|electronic purse]]" systems store funds on the card, so that readers do not need network connectivity. They entered European service in the mid-1990s. They have been common in Germany ([[Geldkarte]]), Austria ([[Quick Wertkarte]]), Belgium ([[Proton (bank card)|Proton]]), France ([[Moneo]]<ref>[http://www.moneo.net Moneo's website] {{Webarchive|url=https://web.archive.org/web/20100208224418/http://www.moneo.net/ |date=8 February 2010 }} (in French).</ref>), the Netherlands ([[Chipknip]] Chipper (decommissioned in 2015)), Switzerland ("Cash"), Norway ("[[Mondex]]"), Spain ("Monedero 4B"), Sweden ("Cash", decommissioned in 2004), Finland ("Avant"), UK ("Mondex"), Denmark ("Danmønt") and Portugal ("Porta-moedas Multibanco").
Private electronic purse systems have also been deployed such as the Marines corps (USMC) at Parris Island allowing small amount payments at the cafeteria.

Since the 1990s, smart cards have been the [[subscriber identity module]]s (SIMs) used in [[GSM]] mobile-phone equipment. Mobile phones are widely used across the world, so smart cards have become very common.

=== EMV ===
{{further|EMV}}
Europay MasterCard Visa (EMV)-compliant cards and equipment are widespread with the deployment led by European countries. The United States started later deploying the EMV technology in 2014, with the deployment still in progress in 2019.{{update inline|date=May 2026}} Typically, a country's national payment association, in coordination with [[MasterCard]] International, [[Visa Inc.|Visa]] International, [[American Express]] and [[Japan Credit Bureau]] (JCB), jointly plan and implement EMV systems.

Historically, in 1993 several international payment companies agreed to develop smart-card specifications for [[debit card|debit]] and credit cards. The original brands were MasterCard, Visa, and [[Europay]]. The first version of the EMV system was released in 1994. In 1998 the specifications became stable.

EMVCo maintains these specifications. EMVco's purpose is to assure the various financial institutions and retailers that the specifications retain backward compatibility with the 1998 version. EMVco upgraded the specifications in 2000 and 2004.<ref>{{Cite web |url=http://www.emvco.org/ |title=EMVco |access-date=7 January 2006 |archive-date=5 June 2020 |archive-url=https://web.archive.org/web/20200605053314/https://www.emvco.com/ |url-status=live }}</ref>

EMV compliant cards were first accepted into Malaysia in 2005<ref>{{cite news |url=http://www.therakyatpost.com/business/2015/10/14/us-learns-from-malaysia-10-years-later/ |title=US learns from Malaysia, 10 years later |newspaper=The Rakyat Post |access-date=30 December 2016 |archive-date=20 March 2019 |archive-url=https://web.archive.org/web/20190320073413/http://www.therakyatpost.com/business/2015/10/14/us-learns-from-malaysia-10-years-later/ |url-status=dead }}</ref> and later into United States in 2014. MasterCard was the first company that was allowed to use the technology in the United States. The United States has felt pushed to use the technology because of the increase in [[identity theft]]. The credit card information stolen from Target in late 2013 was one of the largest indicators that American credit card information is not safe. Target made the decision on 30 April 2014 that it would try to implement the smart chip technology to protect itself from future credit card identity theft.

Before 2014, the consensus in America was that there were enough security measures to avoid credit card theft and that the smart chip was not necessary. The cost of the smart chip technology was significant, which was why most of the corporations did not want to pay for it in the United States. The debate finally ended when Target sent out a notice<ref>{{Cite web |url=https://corporate.target.com/article/2013/12/important-notice-unauthorized-access-to-payment-ca |title=A message from CEO Gregg Steinhafel about Target's payment card issues |access-date=14 March 2021 |archive-date=25 February 2021 |archive-url=https://web.archive.org/web/20210225030644/https://corporate.target.com/article/2013/12/important-notice-unauthorized-access-to-payment-ca |url-status=live }}</ref> stating unauthorized access to magnetic strips<ref>{{Cite news |url=https://www.npr.org/sections/alltechconsidered/2014/01/23/264910138/target-hack-a-tipping-point-in-moving-away-from-magnetic-stripes |title=Target Hack a Tipping Point in Moving Away from Magnetic Stripes |publisher=NPR |access-date=14 March 2021 |archive-date=13 April 2021 |archive-url=https://web.archive.org/web/20210413132845/https://www.npr.org/sections/alltechconsidered/2014/01/23/264910138/target-hack-a-tipping-point-in-moving-away-from-magnetic-stripes |url-status=live }}</ref> costing Target over 300 million dollars along with the increasing cost of online credit theft was enough for the United States to invest in the technology. The adaptation of EMV's increased significantly in 2015 {{clarify span|text=when the liability shifts occurred in October by the credit card companies.|reason=What “liability shifts”?|date=May 2023}}{{citation needed|date=May 2023}}

=== Development of contactless systems ===
{{see also|Contactless payment}}
''Contactless'' smart cards do not require physical contact between a card and reader. They are becoming more popular for payment and ticketing. Typical uses include mass transit and motorway tolls. Visa and MasterCard implemented a version deployed in 2004–2006 in the U.S., with Visa's current offering called [[Visa Inc.#Visa Contactless (formerly payWave)|Visa Contactless]]. Most contactless fare collection systems are incompatible, though the [[MIFARE]] Standard card from [[NXP Semiconductors]] has a considerable market share in the US and Europe.

Use of "Contactless" smart cards in transport has also grown through the use of low cost chips NXP Mifare Ultralight and paper/card/PET rather than PVC. This has reduced media cost so it can be used for low cost tickets and short term transport passes (up to 1 year typically). The cost is typically 10% that of a PVC smart card with larger memory. They are distributed through vending machines, ticket offices and agents. Use of paper/PET is less harmful to the environment than traditional PVC cards.

Smart cards are also being introduced for identification and entitlement by regional, national, and international organizations. These uses include citizen cards, drivers’ licenses, and patient cards. In Malaysia, the compulsory national ID [[MyKad]] enables eight applications and has 18 million users. Contactless smart cards are part of [[ICAO]] [[biometric passport]]s to enhance security for international travel.

=== Complex smart cards ===

Complex Cards are smart cards that conform to the [[ISO/IEC 7810]] standard and include components in addition to those found in traditional single chip smart cards. Complex Cards were invented by Cyril Lalo and Philippe Guillaud in 1999 when they designed a chip smart card with additional components, building upon the initial concept consisting of using audio frequencies to transmit data patented by Alain Bernard.<ref>{{cite web |last1=Bernard |first1=Alain |title=Electronic telephone device |url=https://patents.google.com/patent/US5182767A/en |website=Google Patents |access-date=29 April 2021 |archive-date=18 March 2022 |archive-url=https://web.archive.org/web/20220318202317/https://patents.google.com/patent/US5182767A/en |url-status=live }}</ref> The first Complex Card prototype was developed collaboratively by Cyril Lalo and Philippe Guillaud, who were working at AudioSmartCard<ref>{{cite web |title=AudioSmartCard |url=https://www.infogreffe.com/entreprise-societe/391975125-audiosmartcard-international-sa-750196B12386.html |website=Infogreffe |publisher=French Commercial Court |access-date=29 April 2021 |archive-date=29 April 2021 |archive-url=https://web.archive.org/web/20210429100222/https://www.infogreffe.com/entreprise-societe/391975125-audiosmartcard-international-sa-750196B12386.html |url-status=live }}</ref> at the time, and Henri Boccia and Philippe Patrice, who were working at [[Gemalto#Gemplus|Gemplus]]. It was ISO 7810-compliant and included a battery, a piezoelectric buzzer, a button, and delivered audio functions, all within a 0.84mm thickness card.

The Complex Card pilot, developed by AudioSmartCard, was launched in 2002 by [[Crédit Lyonnais]], a French financial institution. This pilot featured acoustic tones as a means of authentication. Although Complex Cards were developed since the inception of the smart card industry, they only reached maturity after 2010.

Complex Cards can accommodate various peripherals including:
* One or more buttons,
* A digital keyboard,
* An alphabetic keyboard,
* A touch keyboard,
* A small display, for a dynamic [[Card security code|Card Security Code (CSC)]] for instance,
* A larger digital display, for OTP or balance, QR code
* An alphanumeric display,
* A [[fingerprint sensor]],
* A LED,
* A buzzer or speaker.

While first generation Complex Cards were battery powered, the second generation is battery-free and receives power through the usual card connector and/or induction .

Sound, generated by a buzzer, was the preferred means of communication for the first projects involving Complex Cards. Later, with the progress of displays, visual communication is now present in almost all Complex Cards.

====Functionalities====

Complex Cards support all communication protocols present on regular smart cards: contact, thanks to a contact pad as defined [[ISO/IEC 7816]] standard, contactless following the [[ISO/IEC 14443]] standard, and magstripe.

Developers of Complex Cards target several needs when developing them:
* One Time Password,
* Provide account information,
* Provide computation capabilities,
* Provide a means of transaction security,
* Provide a means of user authentication.

=====One time password=====

A Complex Card can be used to compute a cryptographic value, such as a [[One-time password]]. The One-Time Password is generated by a [[Secure cryptoprocessor|cryptoprocessor]] encapsulated in the card. To implement this function, the crypto processor must be initialized with a seed value, which enables the identification of the OTPs respective of each card. The hash of seed value has to be stored securely within the card to prevent unauthorized prediction of the generated OTPs.

One-Time Passwords generation is based either on incremental values (event based) or on a real time clock (time based). Using clock-based One-Time Password generation requires the Complex Card to be equipped with a [[Real-time clock]].

Complex Cards used to generate One Time Password have been developed for:
* Standard Chartered,<ref>{{cite news |last1=Liau |first1=Yun Qing |title=MasterCard launching banking card with OTP capability |url=https://www.zdnet.com/finance/mastercard-launching-banking-card-with-otp-capability/ |access-date=12 May 2021 |publisher=ZDNet |date=8 November 2012 |archive-date=6 May 2021 |archive-url=https://web.archive.org/web/20210506072844/https://www.zdnet.com/article/mastercard-launching-banking-card-with-otp-capability/ |url-status=live }}</ref> Singapore,
* Bank of America,<ref>{{cite web |last1=GamerStuff |title=CES 2012: Interview Cyril Lalo NagraID Security |url=https://www.youtube.com/watch?v=xIEHHZH9br8 |archive-url=https://ghostarchive.org/varchive/youtube/20211211/xIEHHZH9br8 |archive-date=11 December 2021 |url-status=live |via=YouTube |access-date=12 May 2021 |date=24 January 2012}}{{cbignore }}</ref> USA,
* Erste Bank, Croatia,
* Verisign,<ref>{{cite web |title=Mastercard, Symantec and NagraID Security team up to provide further payment card security features |url=https://www.nagra.com/media-center/press-releases/mastercard-symantec-and-nagraid-security-team-provide-further-payment |website=nagra.com |access-date=12 May 2021 |date=14 February 2011 |archive-date=12 May 2021 |archive-url=https://web.archive.org/web/20210512121504/https://www.nagra.com/media-center/press-releases/mastercard-symantec-and-nagraid-security-team-provide-further-payment |url-status=live }}</ref> USA,
* RSA Security.<ref>{{cite news |title=RSA SecurID SD200 – hardware token Series Specs |url=https://www.cnet.com/products/rsa-securid-sd200-hardware-token-series/ |access-date=12 May 2021 |publisher=CNET |archive-date=12 May 2021 |archive-url=https://web.archive.org/web/20210512101921/https://www.cnet.com/products/rsa-securid-sd200-hardware-token-series/ |url-status=live }}</ref>

=====Account information=====

A Complex Card with buttons can display the balance of one or multiple account(s) linked to the card. Typically, either one button is used to display the balance in the case of a single account card or, in the case of a card linked to multiple accounts, a combination of buttons is used to select a specific account's balance.

For additional security, features such as requiring the user to enter an identification or a security value such as a [[Personal identification number|PIN]] can be added to a Complex Card.

Complex Cards used to provide account information have been developed for:
* Getin Bank, Poland,<ref>{{cite news |last1=Getin Bank |title=Getin Bank – poznaj nową Kartę Display do konta bankowego |url=https://www.youtube.com/watch?v=lek_px4wcXQ |access-date=21 May 2021 |via=YouTube |date=7 June 2013 |language=Polish |archive-date=21 May 2021 |archive-url=https://web.archive.org/web/20210521072345/https://www.youtube.com/watch?v=lek_px4wcXQ |url-status=live }}</ref>
* TEB, Turkey.

The latest generation of battery free, button free, Complex Cards can display a balance or other kind of information without requiring any input from the card holder. The information is updated during the use of the card. For instance, in a transit card, key information such as the monetary value balance, the number of remaining trips or the expiry date of a transit pass can be displayed.

=====Transaction security=====

A Complex Card being deployed as a payment card can be equipped with capability to provide transaction security. Typically, [[online payment]]s are made secure thanks to the [[Card security code|Card Security Code (CSC)]], also known as card verification code (CVC2), or card verification value (CVV2). The card security code (CSC) is a 3 or 4 digits number printed on a credit or debit card, used as a security feature for [[Card not present transaction|card-not-present (CNP)]] payment card transactions to reduce the incidence of fraud.

The Card Security Code (CSC) is to be given to the merchant by the cardholder to complete a card-not-present transaction. The CSC is transmitted along with other transaction data and verified by the card issuer. The [[Payment Card Industry Data Security Standard|Payment Card Industry Data Security Standard (PCI DSS)]] prohibits the storage of the CSC by the merchant or any stakeholder in the payment chain. Although designed to be a security feature, the static CSC is susceptible to fraud as it can easily be memorized by a shop attendant, who could then use it for fraudulent online transactions or sale on the dark web.

This vulnerability has led the industry to develop a Dynamic Card Security Code (DCSC) that can be changed at certain time intervals, or after each contact or contactless EMV transaction. This Dynamic CSC brings significantly better security than a static CSC.

The first generation of Dynamic CSC cards, developed by NagraID Security required a battery, a quartz and Real Time Clock (RTC) embedded within the card to power the computation of a new Dynamic CSC, after expiration of the programmed period.

The second generation of Dynamic CSC cards, developed by Ellipse World, Inc., does not require any battery, quartz, or RTC to compute and display the new dynamic code. Instead, the card obtains its power either through the usual card connector or by induction during every EMV transaction from the Point of Sales (POS) terminal or Automated Teller Machine (ATM) to compute a new DCSC.

The Dynamic CSC, also called dynamic cryptogram, is marketed by several companies, under different brand names:
* MotionCode, first developed by NagraID Security, a company later acquired by [[IDEMIA]],
* DCV, the solution offered by [[Gemalto|Thales]],
* EVC (Ellipse Verification Code) by Ellipse, a Los Angeles, USA based company.

The advantage of the Dynamic Card Security Code (DCSC) is that new information is transmitted with the payment transactions, thus making it useless for a potential fraudster to memorize or store it. A transaction with a Dynamic Card Security Code is carried out exactly the same way, with the same processes and use of parameters as a transaction with a static code in a card-not-present transaction. Upgrading to a DCSC allows cardholders and merchants to continue their payment habits and processes undisturbed.

=====User authentication=====

Complex Cards can be equipped with biometric sensors allowing for stronger user authentication. In the typical use case, fingerprint sensors are integrated into a payment card to bring a higher level of user authentication than a PIN.

To implement user authentication using a fingerprint enabled smart card, the user has to authenticate himself/herself to the card by means of the fingerprint before starting a payment transaction.

Several companies<ref>{{cite web |last1=D'Albore |first1=Antonio |title=The rise of biometric cards |date=5-6 October 2017 |url=http://icma.com/wp-content/uploads/2017/10/The-Rise-of-Biometric-Cards10-4.pdf |website=International Card Manufacturers Association |publisher=Embedded Security News |access-date=26 October 2021 |archive-date=26 October 2021 |archive-url=https://web.archive.org/web/20211026234345/http://icma.com/wp-content/uploads/2017/10/The-Rise-of-Biometric-Cards10-4.pdf |url-status=live }}</ref> offer cards with fingerprint sensors, including:
* [[Gemalto|Thales]]: Biometric card,
* [[IDEMIA]]: F.Code, originally developed by NagraID Security,
* [[IDEX Biometrics]],
* [[NXP Semiconductors]]

====Components====

Complex Cards can incorporate a wide variety of components. The choice of components drives functionality, influences cost, power supply needs, and manufacturing complexity.

=====Buttons=====

Depending on Complex Card types, buttons have been added to allow an easy interaction between the user and the card. Typically, these buttons are used to:
* Select one action, such as which account to obtain the balance, or the unit (''e.g.'' currency or number of trips) in which the information is displayed,
* Enter numeric data via the addition of a digital keypad,
* Enter text data via the addition of an alphanumeric keyboard.

While [[Membrane keyboard|separate keys]] have been used on prototypes in the early days, capacitive keyboards are the most popular solution now, thanks to technology developments by AudioSmartCard International SA.<ref>{{cite web |title=Infogreffe – AudioSmartCard International SA |url=https://www.infogreffe.com/entreprise-societe/391975125-audiosmartcard-international-sa-750196B12386.html |website=Infogreffe |publisher=French corporate register |access-date=12 June 2021 |archive-date=1 May 2021 |archive-url=https://web.archive.org/web/20210501035129/https://www.infogreffe.com/entreprise-societe/391975125-audiosmartcard-international-sa-750196B12386.html |url-status=live }}</ref>

The interaction with a capacitive keyboard requires constant power, therefore a battery and a mechanical button are required to activate the card.

=====Buzzer=====

The first Complex Cards were equipped with a buzzer that made it possible to broadcast sound. This feature was generally used over the phone to send identification data such as an identifier and one-time passwords (OTPs). Technologies used for sound transmission include DTMF ([[dual-tone multi-frequency signaling]]) or FSK ([[frequency-shift keying]]).

Companies that offered cards with buzzers include:
* AudioSmartCard,
* nCryptone,<ref>{{cite web |title=Bloomberg – nCryptone |url=https://www.bloomberg.com/profile/company/758050Z:FP |website=Bloomberg |access-date=12 June 2021 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019090211/https://www.bloomberg.com/profile/company/758050Z:FP |url-status=live }}</ref>
* Prosodie,
* Société d'exploitation du jeton sécurisé – SEJS.

=====Display=====

Displaying data is an essential part of Complex Card functionalities. Depending on the information that needs to be shown, displays can be digital or alphanumeric and of varying lengths. Displays can be located either on the front or back of the card. A front display is the most common solution for showing information such as a One-Time Password or an electronic purse balance. A rear display is more often used for showing a Dynamic Card Security Code (DCSC).

Displays can be made using two technologies:
* [[Liquid-crystal display]] (LCD) : LCDs are easily available from a wide variety of suppliers, and they are able to display either digits or alphabetical data. However, to be fitted in a complex smart card, LCDs need to have a certain degree of flexibility. Also, LCDs need to be powered to keep information displayed.
* [[Liquid-crystal display#"Zero-power" (bistable) displays|Bistable displays]], also known as [[Ferroelectric liquid crystal display]]s, are increasingly used as they only require power to refresh the displayed information. The displayed data remains visible, without the need for of any power supply. Bistable displays are also available in a variety of specifications, displaying digits or pixels. Bistable displays are available from E Ink Corporation<ref>{{cite web |title=E Ink |url=https://www.eink.com/index.html |website=E Ink |access-date=12 June 2021 |archive-date=30 July 2021 |archive-url=https://web.archive.org/web/20210730164908/https://www.eink.com/index.html |url-status=live }}</ref> among others.

=====Cryptoprocessor=====

If a Complex smart Card is dedicated to making cryptographic computations (such as generating a one-time password) it may require a [[secure cryptoprocessor]].

=====Power supply=====

As Complex Cards contain more components than traditional smart cards, their power consumption must be carefully monitored.

First generation Complex Cards require a power supply even in standby mode. As such, product designers generally included a battery in their design. Incorporating a battery creates an additional burden in terms of complexity, cost, space and flexibility in an already dense design. Including a battery in a Complex Card increases the complexity of the manufacturing process as a battery cannot be hot laminated.

Second generation Complex Cards feature a battery-free design. These cards harvest the necessary power from external sources; for example when the card interacts in a contact or [[Electromagnetic induction|contactless]] fashion with a payment system or an NFC-enabled smartphone. The use of a bistable display in the card design ensures that the screen remains legible even when the Complex Card is unconnected to the power source.

====Manufacturing====

Complex Card manufacturing methods are inherited from the smart card industry and from the electronics mounting industry. As Complex Cards incorporate several components while having to remain within 0.8 mm thickness and be flexible, and to comply with the [[ISO/IEC 7810]], [[ISO/IEC 7811]] and [[ISO/IEC 7816]] standards, renders their manufacture more complex than standard smart cards.

One of the most popular manufacturing processes in the smart card industry is lamination. This process involves laminating an inlay between two card faces. The inlay contains the needed electronic components with an antenna printed on an inert support.

Typically battery-powered Complex Cards require a cold lamination manufacturing process. This process impacts the manufacturing lead time and the whole cost of such a Complex Card.

Second generation, battery-free Complex Cards can be manufactured by existing hot lamination process. This automated process, inherited from traditional smart card manufacturing, enables the production of Complex Cards in large quantities while keeping costs under control, a necessity for the evolution from a niche to a mass market.

====Card life cycle====

As with standard smart cards, Complex Cards go through a lifecycle comprising the following steps:
* Manufacturing,
* Personalization,
* User enrollment, if needed by the application,
* Provisioning,
* Active life,
* Cancellation,
* Recycling / destruction.

As Complex Cards bring more functionalities than standard smart cards and, due to their complexity, their personalization can take longer or require more inputs. Having Complex Cards that can be personalized by the same machines and the same processes as regular smart cards allows them to be integrated more easily in existing manufacturing chains and applications.

First generation, battery-operated Complex Cards require specific [[Battery recycling|recycling]] processes, mandated by different regulatory bodies. Additionally, keeping battery-operated Complex Cards in inventory for extended periods of time may reduce their performance due to [[Capacity loss|battery ageing]].

Second-generation battery-free technology ensures operation during the entire lifetime of the card and eliminates self-discharge, providing [[extended shelf life]], and is more eco-friendly.

===History and major players===

Since the inception of smart cards, innovators have been trying to add extra features. As technologies have matured and have been industrialized, several smart card industry players have been involved in Complex Cards.

The Complex Card concept began in 1999 when Cyril Lalo and Philippe Guillaud, its inventors, first designed a smart card with additional components. The first prototype was developed collaboratively by Cyril Lalo, who was the CEO of AudioSmartCard at the time, and Henri Boccia and Philippe Patrice, from Gemplus. The prototype included a button and audio functions on a 0.84mm thick ISO 7810-compliant card .

Since then, Complex Cards have been mass-deployed primarily by NagraID Security.

====AudioSmartCard====

AudioSmartCard International SA<ref>{{cite web |title=Company Information AudioSmartCard International SA |url=https://www.infogreffe.com/entreprise-societe/391975125-audiosmartcard-international-sa-750196B12386.html |website=Infogreffe |publisher=French Registries at Commercial Courts |access-date=16 July 2021 |archive-date=19 September 2021 |archive-url=https://web.archive.org/web/20210919164232/https://www.infogreffe.com/entreprise-societe/391975125-audiosmartcard-international-sa-750196B12386.html |url-status=live }}</ref> was instrumental in developing the first Complex Card that included a battery, a piezoelectric buzzer, a button, and audio functions all on a 0.84mm thick, ISO 7810-compatible card.

AudioSmartCard was founded in 1993 and specialized in the development and marketing of acoustic tokens incorporating security features. These acoustic tokens exchanged data in the form of sounds transmitted over a phone line. In 1999, AudioSmartCard transitioned to a new leadership under Cyril Lalo and Philippe Guillaud, who also became major shareholders. They made AudioSmartCard evolve towards the smart card world. In 2003 Prosodie,<ref>{{cite web |title=Information about Prosodie Corporation |url=https://www.infogreffe.fr/entreprise-societe/411393218-prosodie-920197B043840000/liste-etablissements-1.html |website=Infogreffe |publisher=French commercial court registries |access-date=16 July 2021 |archive-date=8 December 2021 |archive-url=https://web.archive.org/web/20211208164642/https://www.infogreffe.fr/entreprise-societe/411393218-prosodie-920197B043840000/liste-etablissements-1.html |url-status=live }}</ref> a subsidiary of [[Capgemini]], joined the shareholders of AudioSmartCard.

AudioSmartCard was renamed nCryptone,<ref>{{cite web |title=nCryptone Corporate Profile |url=https://www.bloomberg.com/profile/company/758050Z:FP |website=Bloomberg |access-date=16 July 2021 |archive-date=19 October 2021 |archive-url=https://web.archive.org/web/20211019090211/https://www.bloomberg.com/profile/company/758050Z:FP |url-status=live }}</ref> in 2004.

====CardLab Innovation====

CardLab Innovation,<ref>{{cite web |title=CardLab Innovation |url=https://www.cardlab.com/ |website=CardLab Innovation |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716172300/https://www.cardlab.com/ |url-status=live }}</ref> incorporated in 2006 in Herlev, Denmark, specializes in Complex Cards that include a switch, a biometric reader, an [[RFID]] jammer, and one or more magstripes. The company works with manufacturing partners in China and Thailand and owns a card lamination factory in Thailand.

====Coin====

Coin was a US-based startup<ref>{{cite web |last1=Cipriani |first1=Jason |title=Coin adds NFC capabilities to its new all-in-one card |url=https://fortune.com/2015/08/27/coin-nfc-update/ |work=Fortune |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716172252/https://fortune.com/2015/08/27/coin-nfc-update/ |url-status=live }}</ref> founded in 2012 by Kanishk Parashar.<ref>{{cite web |title=LinkedIn: Kanishk Parashar |url=https://www.linkedin.com/in/diamondk/ |publisher=LinkedIn }}</ref> It developed a Complex Card capable of storing the data of several credit and debit cards. The card prototype was equipped with a display<ref>{{cite web |last1=Statt |first1=Nick |date=14 November 2013 |title=Inside Coin's techie vision for the all-in-one credit card |url=https://www.cnet.com/tech/mobile/inside-coins-techie-vision-for-the-all-in-one-credit-card/ |publisher=CNET |access-date=11 August 2024 }}</ref>{{Full citation needed|date=July 2021}} and a button that enabled the user to switch between different cards. In 2015, the original Coin card concept evolved into Coin 2.0 adding contactless communication to its original magstripe emulation.<ref>{{cite web |last1=Statt |first1=Nick |title=Coin adds NFC capabilities to its new all-in-one card |url=https://www.cnet.com/tech/mobile/inside-coins-techie-vision-for-the-all-in-one-credit-card/ |publisher=CNET |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716172252/https://www.cnet.com/tech/mobile/inside-coins-techie-vision-for-the-all-in-one-credit-card/ |url-status=live }}</ref>

Coin was acquired by [[Fitbit]] in May 2016<ref>{{cite web |last1=Cooper |first1=Daniel |title=Fitbit buys Coin to help with mobile payments |url=https://www.engadget.com/2016-05-18-fitbit-buys-coin.html |work=Engadget |date=18 May 2016 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716172252/https://www.engadget.com/2016-05-18-fitbit-buys-coin.html |url-status=live }}</ref> and all Coin activities were discontinued in February 2017.<ref>{{cite web |last1=Heater |first1=Brian |title=Coin will shut down its product services at the end of February |url=https://techcrunch.com/2017/01/31/coin-shut-down/?guccounter=1 |website=TechCrunch |date=31 January 2017 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716172254/https://techcrunch.com/2017/01/31/coin-shut-down/?guccounter=1 |url-status=live }}</ref>

====Ellipse World, Inc.====

Ellipse World, Inc.<ref>{{cite web |title=Ellipse World Inc. |url=https://www.ellipse.la/ |website=Ellipse World Inc. |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716173249/https://www.ellipse.la/ |url-status=live }}</ref> was founded in 2017 by Cyril Lalo and Sébastien Pochic, both recognized experts in Complex Card technology. Ellipse World, Inc. specializes in battery-free Complex Card technology.

The Ellipse patented technologies enable smart card manufacturers to use their existing dual interface payment card manufacturing process and supply chain to build battery-free, second generation Complex Cards with display capabilities. Thanks to this ease of integration, smart card vendors are able to address banking, transit and prepaid cards markets.

====EMue Technologies====

EMue<ref>{{cite web |title=Emue Technologies |url=http://www.emue.com/ |website=Emue Technologies |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716173249/http://www.emue.com/ |url-status=live }}</ref> Technologies, headquartered in Melbourne, Australia, designed and developed authentication solutions for the financial services industry from 2009 to 2015.<ref>{{cite web |title=LinkedIn: Emue Technologies |url=https://www.linkedin.com/company/emue-technologies/about/ |publisher=LinkedIn |access-date=16 July 2021 }}</ref> The company's flagship product, developed in collaboration with Cyril Lalo and Philippe Guillaud, was the eMue Card, a Visa CodeSure<ref>{{cite web |title=Visa CodeSure gets commercial green light |url=https://www.finextra.com/newsarticle/21447/visa-codesure-gets-commercial-green-light |website=Finextra |date=2 June 2010 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716173249/https://www.finextra.com/newsarticle/21447/visa-codesure-gets-commercial-green-light |url-status=live }}</ref> credit card with an embedded keypad, a display and a microprocessor.

====Feitian Technologies====

Feitian Technologies, a China-based company created in 1998, provides cyber security products and solutions. The company offers security solutions based on smart cards as well as other authentication devices. These include Complex Cards, that incorporate a display,<ref>{{cite web |title=OTP Display Card |url=https://www.ftsafe.com/Products/Power_Card/Standard |website=Feitian technologies |access-date=16 July 2021 |archive-date=13 August 2021 |archive-url=https://web.archive.org/web/20210813022959/https://www.ftsafe.com/Products/Power_Card/Standard |url-status=live }}</ref> a keypad<ref>{{cite web |title=Chip Embedded Card |url=https://www.ftsafe.com/Products/Power_Card/Chip |website=Feitian Technologies |access-date=16 July 2021 |archive-date=24 June 2021 |archive-url=https://web.archive.org/web/20210624082728/https://www.ftsafe.com/Products/Power_Card/Chip |url-status=live }}</ref> or a fingerprint sensor.<ref>{{cite web |title=OTP Display Card |url=https://www.ftsafe.com/Products/Power_Card/Fingerprint |website=Feitian Technologies |access-date=16 July 2021 |archive-date=1 August 2021 |archive-url=https://web.archive.org/web/20210801225611/https://www.ftsafe.com/Products/Power_Card/Fingerprint |url-status=live }}</ref>

====Fingerprint Cards====

[[Fingerprint Cards]] AB (or Fingerprints<ref>{{cite web |title=Fingerprint Cards |url=https://www.fingerprints.com/ |website=Fingerprint Cards |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716174136/https://www.fingerprints.com/ |url-status=live }}</ref>) is a Swedish company specializing in biometric solutions. The company sells biometric sensors and has recently introduced payment cards incorporating a fingerprint sensor<ref>{{cite web |title=Biometrics: The missing piece of the contactless card puzzle |url=https://www.fingerprints.com/uploads/2018/05/fpc-smartcards-infographics-v1.pdf |website=Fingerprint Cards |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716174140/https://www.fingerprints.com/uploads/2018/05/fpc-smartcards-infographics-v1.pdf |url-status=live }}</ref> such as the Zwipe card,<ref>{{cite web |title=Zwipe Payment Card the World's Leading Biometric Payment Card |url=https://www.fingerprints.com/showcase/zwipe-payment-card/ |website=Fingerprint Cards |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716174137/https://www.fingerprints.com/showcase/zwipe-payment-card/ |url-status=live }}</ref> a biometric dual-interface payment card using an integrated sensor from Fingerprints.

====Giesecke+Devrient====

[[Giesecke+Devrient|Giesecke & Devrient]], also known as G+D,<ref>{{cite web |title=Giesecke+Devrient |url=https://www.gi-de.com/en/ |website=Giesecke+Devrient |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716074938/https://www.gi-de.com/en/ |url-status=live }}</ref> is a German company headquartered in Munich that provides banknotes, security printing, smart cards and cash handling systems. Its smart card portfolio includes display cards, OTP cards, as well as cards displaying a [[#Transaction_security|Dynamic CSC]].

====Gemalto====

[[Gemalto]], a division of [[Thales Group]], is a major player in the secure transaction industry.
The company's Complex Card portfolio includes cards with a display<ref>{{cite web |title=Payments |url=https://www.gemalto.com/financial/cards/payments |website=Thales Group – Gemalto |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180007/https://www.gemalto.com/financial/cards/payments |url-status=live }}</ref> or a fingerprint sensor.<ref>{{cite web |title=EMV Biometric Card |url=https://www.gemalto.com/financial/cards/emv-biometric-card |website=Thales Group – Gemalto |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180005/https://www.gemalto.com/financial/cards/emv-biometric-card |url-status=live }}</ref> These cards may display an OTP<ref>{{cite web |title=SafeNet OTP Display Card |url=https://cpl.thalesgroup.com/access-management/authenticators/safenet-otp-display-card |website=Thales Group – SafeNet |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180005/https://cpl.thalesgroup.com/access-management/authenticators/safenet-otp-display-card |url-status=live }}</ref> or a Dynamic CSC.<ref>{{cite web |title=Dynamic Code Verification |url=https://www.gemalto.com/financial/cards/payments/dynamic-code-verification |website=Thales Group – Gemalto |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180005/https://www.gemalto.com/financial/cards/payments/dynamic-code-verification |url-status=live }}</ref>

====Idemia====

[[IDEMIA]] is the product of the 2017<ref>{{cite web |title=Oberthur Technologies –Morpho becomes IDEMIA, the global leader in trusted identities |url=https://www.idemia.com/public_download/oberthur-technologies-morpho-becomes-idemia-global-leader-trusted-identities |website=Idemia |date=28 September 2017 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180009/https://www.idemia.com/public_download/oberthur-technologies-morpho-becomes-idemia-global-leader-trusted-identities |url-status=live }}</ref> merger of Oberthur Technologies and Morpho. The combined company has positioned itself as a global provider of financial cards, SIM cards, biometric devices as well as public and private identity solutions. Due to Oberthur's acquisition of NagraID Security in 2014, Idemia's Complex Card offerings include the F.CODE<ref>{{cite web |title=Biometric payment card |url=https://www.idemia.com/biometric-payment-card |website=Idemia |date=17 September 2020 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180005/https://www.idemia.com/biometric-payment-card |url-status=live }}</ref> biometric payment card that includes a fingerprint sensor, and its battery-powered Motion Code<ref>{{cite web |title=Motion Code |url=https://www.idemia.com/motion-code |website=Idemia |date=13 October 2020 |access-date=16 July 2021 |archive-date=22 June 2021 |archive-url=https://web.archive.org/web/20210622214427/https://www.idemia.com/motion-code |url-status=live }}</ref> card that displays a Dynamic CSC.

====Idex====

[[IDEX Biometrics]] ASA, incorporated in Norway, specializes in fingerprint identification technologies for personal authentication. The company offers fingerprint sensors<ref>{{cite web |title=Fingerprint sensor manufacturer |url=https://www.idexbiometrics.com/products/biometric-fingerprint-sensors/ |website=Idex Biometrics |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180008/https://www.idexbiometrics.com/products/biometric-fingerprint-sensors/ |url-status=live }}</ref> and modules<ref>{{cite web |title=What is a fingerprint sensor module? |url=https://www.idexbiometrics.com/faq/fingerprint-sensors/what-is-a-fingerprint-sensor-module/ |website=Idex Biometrics |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180005/https://www.idexbiometrics.com/faq/fingerprint-sensors/what-is-a-fingerprint-sensor-module/ |url-status=live }}</ref> that are ready to be embedded into cards.<ref>{{cite web |title=XH Smart Tech showcasing dual-interface biometric card with IDEX sensor at Mobile World Congress in Barcelona |url=https://www.idexbiometrics.com/xh-smart-tech-showcasing-dual-interface-biometric-card-with-idex-sensor-at-mobile-world-congress-in-barcelona/ |website=Idex Biometrics |date=25 February 2019 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716180005/https://www.idexbiometrics.com/xh-smart-tech-showcasing-dual-interface-biometric-card-with-idex-sensor-at-mobile-world-congress-in-barcelona/ |url-status=live }}</ref>

====Innovative Card Technologies====

Founded in 2002, by Alan Finkelstein, Innovative Card Technologies developed and commercialized enhancements for the smart card market. The company acquired the display card assets of nCryptone<ref>{{cite news |title=nCryptone monte au capital d'Innovative Card Technologies |url=https://www.journaldunet.com/solutions/dsi/1066019-ncryptone-monte-au-capital-d-innovative-card-technologies/ |access-date=16 July 2021 |publisher=JDN |date=30 June 2006 |language=French |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716181454/https://www.journaldunet.com/solutions/dsi/1066019-ncryptone-monte-au-capital-d-innovative-card-technologies/ |url-status=live }}</ref> in 2006. Innovative Card Technologies has ceased its activities.

====NagraID====

Nagra ID, now known as NID,<ref>{{cite web |title=NID |url=https://www.nagraid.com/ |website=NID |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716181454/https://www.nagraid.com/ |url-status=live }}</ref> was a wholly owned subsidiary of the [[Kudelski Group]] until 2014. NID can trace its history with Complex Cards back to 2003 when it collaborated on development with nCryptone. Nagra ID was instrumental in developing the cold lamination process for Complex Cards manufacturing.

Nagra ID manufactures Complex Cards<ref>{{cite web |title=Complex Cards |url=https://www.nagraid.com/en/solutions/complex-cards |website=NID |access-date=16 July 2021 |archive-date=18 September 2021 |archive-url=https://web.archive.org/web/20210918063258/https://www.nagraid.com/en/solutions/complex-cards |url-status=live }}</ref> that can include a battery, buttons, displays or other electronic components.

====NagraID Security====

Nagra ID Security began in 2008 as a spinoff of Nagra ID to focus on Complex Card development and manufacturing. The company was owned by [[Kudelski Group]] (50%), Cyril Lalo (25%) and Philippe Guillaud (25%).

NagraID Security quickly became a leading player in the adoption of Complex Cards due, in large part, to its development of MotionCode cards that featured a small display to enable a [[Card security code|Card Security Code (CVV2)]].

NagraID Security was the first Complex Cards manufacturer to develop a mass market for payment display cards. Their customers included:
* ABSA,<ref>{{cite web |title=MasterCard and Absa Introduce Next Generation Payment Card, a First for APMEA |url=https://newsroom.mastercard.com/press-releases/mastercard-and-absa-introduce-next-generation-payment-card-a-first-for-apmea/ |website=MasterCard |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716181453/https://newsroom.mastercard.com/press-releases/mastercard-and-absa-introduce-next-generation-payment-card-a-first-for-apmea/ |url-status=live }}</ref> South Africa,
* Banco Bicentenario, Venezuela,
* Banco MontePaschi, Belgium,
* Erste Bank, Croatia,
* Getin Bank, Poland,
* Standard Chartered Bank, Singapore.

NagraID Security also delivered One-Time Password cards to companies including:
* Bank of America,
* HID Security,
* PayPal,
* RSA Security,
* Verisign.

In 2014, NagraID Security was sold to [[Oberthur Technologies]] (now [[IDEMIA]]).

====nCryptone====

nCryptone emerged in 2004 from the renaming of AudioSmartCard. nCryptone was headed by Cyril Lalo and Philippe Guillaud<ref>{{cite web |title=Philippe Guillaud |url=https://www.epita.fr/2018/11/26/temoignage-ancien-ingenieur-entrepreneur-muzeek-intelligence-artificielle-musique-entreprises-parcours-2018/ |website=Epita |date=26 November 2018 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716182629/https://www.epita.fr/2018/11/26/temoignage-ancien-ingenieur-entrepreneur-muzeek-intelligence-artificielle-musique-entreprises-parcours-2018/ |url-status=live }}</ref> and developed technologies around authentication servers and devices.

nCryptone display card assets were acquired by Innovative Card Technologies in 2006.<ref>{{cite news |title=nCryptone acquiert IC Tech |url=https://investir.lesechos.fr/actions/actualites/ncryptone-acquiert-ic-tech-141099.php |access-date=16 July 2021 |publisher=Les Echos Investir |date=30 June 2006 |language=French |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716182631/https://investir.lesechos.fr/actions/actualites/ncryptone-acquiert-ic-tech-141099.php |url-status=live }}</ref>

====Oberthur Technologies, now Idemia====

[[Oberthur Technologies]], now [[IDEMIA]], is one of the major players in the secure transactions industry. It acquired the business of NagraID Security in 2014. Oberthur then merged with Morpho and the combined entity was renamed Idemia in 2017.

Major references in the Complex Cards business include:
* BPCE Group,<ref>{{cite web |title=BPCE Group and Oberthur Technologies launch a world-exclusive innovation: the first dynamic cryptogram payment card |url=https://newsroom-en.groupebpce.fr/news/bpce-group-and-oberthur-technologies-launch-a-world-exclusive-innovation-the-first-dynamic-cryptogram-payment-card-e9bc-53927.html |website=BPCE |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716182631/https://newsroom-en.groupebpce.fr/news/bpce-group-and-oberthur-technologies-launch-a-world-exclusive-innovation-the-first-dynamic-cryptogram-payment-card-e9bc-53927.html |url-status=live }}</ref> France,
* Orange Bank,<ref>{{cite news |title=Orange Bank : une carte Visa Premium avec cryptogramme dynamique et Apple Pay |url=https://www.igen.fr/ailleurs/2019/03/orange-bank-une-carte-visa-premium-avec-cryptogramme-dynamique-et-apple-pay-107063 |access-date=16 July 2021 |publisher=iGen |date=7 March 2019 |language=French |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716182640/https://www.igen.fr/ailleurs/2019/03/orange-bank-une-carte-visa-premium-avec-cryptogramme-dynamique-et-apple-pay-107063 |url-status=live }}</ref> France,
* Société Générale,<ref>{{cite web |title=1 million MOTION CODE online transactions with Société Générale |url=https://www.idemia.com/press-release/1-million-motion-code-online-transactions-societe-generale-2017-10-17 |website=Idemia |date=17 October 2017 |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716182631/https://www.idemia.com/press-release/1-million-motion-code-online-transactions-societe-generale-2017-10-17 |url-status=live }}</ref> France.

====Plastc====

Set up in 2009, Plastc announced a single card that could digitally hold the data of up to 20 credit or debit cards. The company succeeded in raising US$9 million through preorders but failed to deliver any product.<ref>{{cite news |last1=Schubarth |first1=Cromwell |title=Palo Alto 'smart' credit card startup shutters after taking $9M in pre-orders |url=https://www.bizjournals.com/sanjose/news/2017/04/21/palo-alto-smartcredit-card-startup-shutters-after.html |access-date=16 July 2021 |publisher=Biz Journals |date=21 April 2017 |archive-date=19 December 2020 |archive-url=https://web.archive.org/web/20201219114135/http://www.bizjournals.com/sanjose/news/2017/04/21/palo-alto-smartcredit-card-startup-shutters-after.html |url-status=live }}</ref> Plastc was then acquired<ref>{{cite magazine |title=Edge Mobile Payments Acquires Plastc Assets |url=https://edgemobilepayments.com/edge-mobile-payments-acquires-plastc |magazine=Edge |access-date=16 July 2021 }}</ref> in 2017 by Edge Mobile Payments,<ref>{{cite web |title=Edge Mobile Payments |url=https://edgemobilepayments.com/ |website=Edge Mobile Payments |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716183707/https://edgemobilepayments.com/ |url-status=live }}</ref> a Santa Cruz-based Fintech company. The Plastc project continues as the Edge card,<ref>{{cite web |title=EDGE Mobile Payments Announces Development of the EDGE Card |url=https://edgemobilepayments.com/edge-mobile-payments-announces-development-of-the-edge-card |website=EDGE Mobile Payments |access-date=16 July 2021 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716183706/https://edgemobilepayments.com/edge-mobile-payments-announces-development-of-the-edge-card |url-status=live }}</ref> a dynamic payment card that consolidates several payment cards in one device. The card is equipped with a battery and an ePaper screen and can store data from up to 50 credit, debit, loyalty and gift cards.

====Stratos====

Stratos<ref>{{cite web |title=Stratos |url=https://cardlabcards.com/ |website=Stratos |access-date=16 July 2021 |archive-date=6 May 2021 |archive-url=https://web.archive.org/web/20210506072528/https://www.cardlabcards.com/ |url-status=live }}</ref> was created in 2012 in Ann Arbor, Michigan, USA. In 2015, Stratos developed the Stratos Bluetooth Connected Card,<ref>{{cite news |last1=Cipriani |first1=Jason |title=One card to rule them all? Stratos smart card replaces the need for a wallet |url=https://fortune.com/2015/05/13/stratos-smart-card/ |access-date=16 July 2021 |work=Fortune |date=13 May 2015 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716184616/https://fortune.com/2015/05/13/stratos-smart-card/ |url-status=live }}</ref> which was designed to integrate up to three credit and debit card in a single card format and featured a smartphone app used to manage the card. Due to its Lithium ion thin film battery, the Stratos card was equipped with LEDs and communicated in contactless mode and in Bluetooth low Energy.

In 2017 Stratos was acquired<ref>{{cite web |title=Stratos Connected Card Platform Acquired by CardLab Innovations |url=https://cardlabcards.com/blog/2017/02/15/cardlab-acquisition-announcement/ |website=Stratos |access-date=16 July 2021 |archive-date=12 March 2021 |archive-url=https://web.archive.org/web/20210312101258/https://cardlabcards.com/blog/2017/02/15/cardlab-acquisition-announcement/ |url-status=live }}</ref> by CardLab Innovation, a company headquartered in Herlev, Denmark.

====Swyp====

SWYP<ref>{{cite web |title=Swyp |url=https://www.swypcard.com/ |website=Swyp |access-date=16 July 2021 |archive-date=28 July 2021 |archive-url=https://web.archive.org/web/20210728204610/https://www.swypcard.com/ |url-status=live }}</ref> was the brand name of a card developed by Qvivr, a company incorporated in 2014 in Fremont, California. SWYP was introduced in 2015 and dubbed the world's first smart wallet. SWYP was a metal card with the ability to combine over 25 credit, debit, gift and loyalty cards. The card worked in conjunction with a smartphone app used to manage the cards. The Swyp card included a battery, a button and a matrix display that showed which card was in use. The company registered users in its beta testing program, but the product never shipped on a commercial scale.

Qvivr raised US$5 million in January 2017<ref>{{cite news |last1=Magistretti |first1=Bérénice |title=Mobile payment startup Qvivr raises $5 million led by Khosla Ventures |url=https://venturebeat.com/2017/01/31/mobile-payment-startup-qvivr-raises-5-million-led-by-khosla-ventures/ |access-date=16 July 2021 |publisher=VentureBeat |date=31 January 2017 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716184611/https://venturebeat.com/2017/01/31/mobile-payment-startup-qvivr-raises-5-million-led-by-khosla-ventures/ |url-status=live }}</ref> and went out of business in November 2017.

===Businesses===

Complex Cards have been adopted by numerous financial institutions worldwide. They may include different functionalities such as payment cards (credit, debit, prepaid), [[One-time password]], mass-transit, and dynamic [[Card security code|Card Security Code (CVV2)]].

Complex Card technology is used by numerous financial institutions including:
* ABSA,<ref>{{cite web |title=MasterCard and Absa Introduce Next Generation Payment Card, a First for APMEA |url=https://newsroom.mastercard.com/press-releases/mastercard-and-absa-introduce-next-generation-payment-card-a-first-for-apmea/ |website=MasterCard |access-date=17 July 2021 |date=28 November 2012 |archive-date=16 July 2021 |archive-url=https://web.archive.org/web/20210716181453/https://newsroom.mastercard.com/press-releases/mastercard-and-absa-introduce-next-generation-payment-card-a-first-for-apmea/ |url-status=live }}</ref> South Africa,
* Banca MontePaschi Belgio,<ref>{{cite web |title=World first for Belgium: Banca Monte Paschi Belgio and MasterCard launch the first payment card combining debit, credit, display screen and contactless payment facilities |url=https://newsroom.mastercard.com/press-releases/world-first-for-belgium-banca-monte-paschi-belgio-and-mastercard-launch-the-first-payment-card-combining-debit-credit-display-screen-and-contactless-payment-facilities/ |website=MasterCard |access-date=17 July 2021 |date=23 October 2012 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180856/https://newsroom.mastercard.com/press-releases/world-first-for-belgium-banca-monte-paschi-belgio-and-mastercard-launch-the-first-payment-card-combining-debit-credit-display-screen-and-contactless-payment-facilities/ |url-status=live }}</ref>
* Bank of America,<ref>{{cite news |title=Bank of America unveils SafePass card |url=https://www.finextra.com/news/announcement.aspx?pressreleaseid=24783 |access-date=17 July 2021 |agency=Finextra |publisher=Finextra |date=24 November 2008 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180857/https://www.finextra.com/news/announcement.aspx?pressreleaseid=24783 |url-status=live }}</ref> USA,
* BPCE Group,<ref>{{cite news |last1=Verdict Staff |title=BPCE, Oberthur to pilot first dynamic cryptogram payment card |url=https://www.cardsinternational.com/news/bpce-oberthur-to-pilot-first-dynamic-cryptogram-payment-card-210515-4582123/ |access-date=17 July 2021 |publisher=Cards International |date=21 May 2015 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180857/https://www.cardsinternational.com/news/bpce-oberthur-to-pilot-first-dynamic-cryptogram-payment-card-210515-4582123/ |url-status=live }}</ref> France,
* Carpatica Bank,<ref>{{cite news |title=Carpatica Bank launches display card in Romania |url=https://business-review.eu/news/carpatica-bank-launches-display-card-in-romania-12929-479 |access-date=17 July 2021 |publisher=Business Review, Romania |date=6 December 2011 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180858/https://business-review.eu/news/carpatica-bank-launches-display-card-in-romania-12929-479 |url-status=live }}</ref> Romania,
* Credit Europe Bank,<ref>{{cite web |title=MasterCard Drives Growth in Its Display Card Programme with Bank Launches in Romania |url=https://newsroom.mastercard.com/press-releases/mastercard-drives-growth-in-its-display-card-programme-with-bank-launches-in-romania/ |website=MasterCard |access-date=17 July 2021 |date=15 November 2011 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180848/https://newsroom.mastercard.com/press-releases/mastercard-drives-growth-in-its-display-card-programme-with-bank-launches-in-romania/ |url-status=live }}</ref> Romania,
* [[Erste & Steiermärkische Bank]],<ref>{{cite web |title=Erste Maestro PayPass Display Card |url=https://ceesca.org/uploads/presentations/09-2013/Erste-CEESCA-zadar.pdf |website=Erste Bank |access-date=17 July 2021 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180849/https://ceesca.org/uploads/presentations/09-2013/Erste-CEESCA-zadar.pdf |url-status=live }}</ref> Croatia
* Getin Bank,<ref>{{cite web |author1=Getin Bank |title=Getin Bank – poznaj nową Kartę Display do konta bankowego |url=https://www.youtube.com/watch?v=lek_px4wcXQ |via=YouTube |access-date=17 July 2021 |language=Polish |format=Video |date=7 June 2013 |archive-date=21 May 2021 |archive-url=https://web.archive.org/web/20210521072345/https://www.youtube.com/watch?v=lek_px4wcXQ |url-status=live }}</ref> Poland,
* Newcastle Banking Society,<ref>{{cite news |last1=Grant |first1=Ian |title=Newcastle Banking Society debuts smart display cards |url=https://www.computerweekly.com/news/1280093009/Newcastle-Banking-Society-debuts-smart-display-cards |access-date=17 July 2021 |work=Computer Weekly |date=14 June 2010 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180848/https://www.computerweekly.com/news/1280093009/Newcastle-Banking-Society-debuts-smart-display-cards |url-status=live }}</ref> UK,
* Orange Bank, France,
* PayPal,<ref>{{cite news |last1=Smith |first1=Josh |title=PayPal security key card – is it worth it? |url=https://www.aol.com/2010/08/04/paypal-security-key-card-offers-extra-security-for-online-paymen/?guccounter=2 |access-date=17 July 2021 |publisher=AOL |date=4 August 2010 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180857/https://www.aol.com/2010/08/04/paypal-security-key-card-offers-extra-security-for-online-paymen/?guccounter=2 |url-status=live }}</ref> USA,
* Sinopac,<ref>{{cite news |title=Taiwan's Bank SinoPac issues credit cards with digital display |url=https://www.finextra.com/news/fullstory.aspx?newsitemid=21900 |access-date=17 July 2021 |publisher=Finextra |date=14 October 2010 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180920/https://www.finextra.com/news/fullstory.aspx?newsitemid=21900 |url-status=live }}</ref> Taiwan,
* Société Générale,<ref>{{cite news |title=1 Million MOTION CODE? Online Transactions With Société Générale |url=https://www.eleconomista.es/empresas-finanzas/noticias/8679977/10/17/1-Million-MOTION-CODE-Online-Transactions-With-Societe-Generale.html |work=El Economista |date=17 October 2017 |access-date=17 July 2021 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180846/https://www.eleconomista.es/empresas-finanzas/noticias/8679977/10/17/1-Million-MOTION-CODE-Online-Transactions-With-Societe-Generale.html |url-status=live }}</ref> France,
* Standard Chartered Bank,<ref>{{cite news |last1=Liau |first1=Yun Qing |title=MasterCard launching banking card with OTP capability |url=https://www.zdnet.com/finance/mastercard-launching-banking-card-with-otp-capability/ |publisher=ZDNet |date=8 November 2012 |access-date=12 May 2021 |archive-date=6 May 2021 |archive-url=https://web.archive.org/web/20210506072844/https://www.zdnet.com/article/mastercard-launching-banking-card-with-otp-capability/ |url-status=live }}</ref><ref>{{cite news |last1=Parrish |first1=Kevin |title=MasterCard Electronic Display Cards Finally Go Mainstream |url=https://www.tomsguide.com/us/MasterCard-Display-Card-Debit-Credit-OTP,news-16282.html |access-date=17 July 2021 |publisher=Tom's Guide |date=8 November 2012 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180857/https://www.tomsguide.com/us/MasterCard-Display-Card-Debit-Credit-OTP,news-16282.html |url-status=live }}</ref> Singapore,
* Symantec,<ref>{{cite news |title=MasterCard, Symantec and NagraID Security team on display card |url=https://www.finextra.com/pressarticle/37871/mastercard-symantec-and-nagraid-security-team-on-display-card |agency=Finextra |publisher=Finextra |date=15 February 2011 |access-date=17 July 2021 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180908/https://www.finextra.com/pressarticle/37871/mastercard-symantec-and-nagraid-security-team-on-display-card |url-status=live }}</ref>
* TEB,<ref>{{cite news |title=Türk Ekonomi Bankası (TEB) has launched a new digital banking service |url=https://cardflash.com/news/2015/04/cepteteb/ |access-date=17 July 2021 |publisher=CardFlash |date=27 April 2015 |archive-date=17 July 2021 |archive-url=https://web.archive.org/web/20210717180848/https://cardflash.com/news/2015/04/cepteteb/ |url-status=live }}</ref> Turkey.

== Design ==
A smart card may have the following generic characteristics:

* Dimensions similar to those of a credit card. ID-1 of the [[ISO/IEC 7810]] standard defines cards as nominally {{convert|85.60|x|53.98|mm|sigfig=3}}. Another popular size is ID-000, which is nominally {{convert|25|x|15|mm}} (commonly used in SIM cards). Both are {{convert|0.76|mm}} thick.
* Contains a [[tamper-resistant]] security system (for example a [[secure cryptoprocessor]] and a secure [[file system]]) and provides security services (e.g., protects in-memory information).
* Managed by an administration system, which securely interchanges information and configuration settings with the card, controlling card [[Blacklist (computing)|blacklisting]] and application-data updates.
* Communicates with external services through card-reading devices, such as ticket readers, [[Automated teller machine|ATM]]s, [[Dip reader]], etc.
* Smart cards are typically made of plastic, generally [[polyvinyl chloride]], but sometimes [[polyethylene terephthalate|polyethylene-terephthalate]]-based [[polyesters]], [[acrylonitrile butadiene styrene]] or [[polycarbonate]].
Since April 2009, a Japanese company has manufactured reusable financial smart cards made from paper.<ref>{{cite news |title=development of the "KAMICARD" IC card made from recyclable and biodegradable paper |url=http://www.toppan.co.jp/english/news/newsrelease883.html |archive-url=https://web.archive.org/web/20090227010101/http://www.toppan.co.jp/english/news/newsrelease883.html |publisher=Toppan Printing Company |archive-date=27 February 2009 |url-status=dead |access-date=27 March 2009 }}</ref>

=== Internal structure ===
==== Data structures ====
As mentioned above, data on a smart card may be stored in a [[file system]] (FS). In smart card file systems, the root directory is called the "master file" ("MF"), subdirectories are called "dedicated files" ("DF"), and ordinary files are called "elementary files" ("EF").<ref name="kilicli-howto">{{cite web |first1=Tolga |last1=Kiliçli |title=Smart Card HOWTO |url=http://linux.com/learn/docs/ldp/750-Smart-Card-HOWTO |archive-url=https://web.archive.org/web/20090615092131/http://linux.com/learn/docs/ldp/750-Smart-Card-HOWTO |date=19 September 2001 |archive-date=15 June 2009 |access-date=28 November 2020 |url-status=dead }}</ref>

==== Logical layout ====
The file system mentioned above is stored on an [[EEPROM]] (storage or memory) within the smartcard.<ref name="kilicli-howto"/> In addition to the EEPROM, other components may be present, depending upon the kind of smartcard. Most smartcards have one of three logical layouts:

* [[EEPROM]] only.
* EEPROM, ROM, RAM, and microprocessor.
* EEPROM, ROM, RAM, microprocessor, and [[secure element]].<ref name="kilicli-howto"/>

In cards with microprocessors, the microprocessor sits inline between the reader and the other components. The operating system that runs on the microprocessor mediates the reader's access to those components to prevent unauthorized access.<ref name="kilicli-howto"/>

=== Physical interfaces ===
==== Contact smart cards ====
[[File:Smartcard chip structure and packaging EN.svg|thumb|Illustration of smart-card structure and packaging]]
[[File:Locale_RS6_Sim Chip.jpg|thumb|4 by 4 mm silicon chip in a SIM card, which was peeled open. Note the thin gold bonding wires and the regular, rectangular digital-memory areas.]]
[[File:SmartCardPinout.svg|thumb|A smart-card [[pinout]]. '''VCC''': [[IC power supply pin|Power supply]]. '''RST''': Reset signal, used to reset the card's communications. '''CLK''': Provides the card with a [[clock signal]], from which data communications timing is derived. '''GND''': [[Ground (electricity)|Ground]] (reference voltage). '''VPP''': ISO/IEC 7816-3:1997 designated this as a programming voltage: an input for a higher voltage to program persistent memory (e.g., [[EEPROM]]). ISO/IEC 7816-3:2006 designates it SPU, for either standard or proprietary use, as input and/or output. '''I/O''': Serial input and output ([[half-duplex]]). '''C4, C8''': The two remaining contacts are AUX1 and AUX2 respectively and are used for [[USB]] interfaces and other uses.<ref>[http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=36576 ISO/IEC 7816-2:1999/Amd 1:2004 ''Assignment of contacts C4 and C8''] {{Webarchive|url=https://web.archive.org/web/20120315031835/http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=36576 |date=15 March 2012 }}.</ref> However, the usage defined in ISO/IEC 7816-2:1999/Amd 1:2004 may have been superseded by ISO/IEC 7816-2:2007.<ref>[http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=45989 ISO/IEC 7816-2:2007. Identification cards – Integrated circuit cards – Part 2: Cards with contacts – Dimensions and location of the contacts] {{Webarchive|url=https://web.archive.org/web/20160304093036/http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=45989 |date=4 March 2016 }}.</ref>]]

[[File:Locale_RS6_Differentsmartcardpadlayouts.jpg|thumb|Contact-type smart cards may have many different [[contact pad]] layouts, such as these [[Subscriber identity module|SIMs]].]]
Contact smart cards have a contact area of approximately {{convert|1|cm2}}, comprising several gold-plated [[contact pad]]s. These pads provide electrical connectivity when inserted into a [[Card reader|reader]],<ref>{{cite web |title=About Smart Cards: Introduction: Primer |url=http://www.smartcardalliance.org/smart-cards-intro-primer/ |publisher=Secure Technology Alliance |access-date=7 August 2017 |archive-date=27 March 2018 |archive-url=https://web.archive.org/web/20180327135443/http://www.smartcardalliance.org/smart-cards-intro-primer/ |url-status=live }}</ref> which is used as a communications medium between the smart card and a host (e.g., a computer, a point of sale terminal) or a mobile telephone. Cards do not contain [[Battery (electricity)|batteries]]; power is supplied by the card reader.

The [[ISO/IEC 7810]] and [[ISO/IEC 7816]] series of standards define:
* physical shape and characteristics,
* electrical connector positions and shapes,
* electrical characteristics,
* [[communications protocol]]s, including commands sent to and responses from the card,
* basic functionality.

Because the chips in financial cards are the same as those used in [[subscriber identity module]]s (SIMs) in mobile phones, programmed differently and embedded in a different piece of [[Polyvinyl chloride|PVC]], chip manufacturers are building to the more demanding GSM/3G standards. So, for example, although the EMV standard allows a chip card to draw 50 mA from its terminal, cards are normally well below the telephone industry's 6 mA limit. This allows smaller and cheaper financial card terminals.

Communication protocols for contact smart cards include T=0 (character-level transmission protocol, defined in ISO/IEC 7816-3) and T=1 (block-level transmission protocol, defined in ISO/IEC 7816-3).

==== Contactless smart cards ====
{{Main|Contactless smart card}}

''Contactless smart cards'' communicate with readers under protocols defined in the [[ISO/IEC 14443]] standard. They support data rates of 106–848 kbit/s. These cards require only proximity to an antenna to communicate.
Like smart cards with contacts, contactless cards do not have an internal power source. Instead, they use a [[loop antenna]] coil to capture some of the incident radio-frequency interrogation signal, [[rectifier|rectify]] it, and use it to power the card's electronics. Contactless smart media can be made with PVC, paper/card and PET finish to meet different performance, cost and durability requirements.

APDU transmission by a contactless interface is defined in [[ISO/IEC 14443]]-4.

==== Hybrids ====
[[File:Locale_RS6_Australia Bank Paypass Card.png|thumb|A hybrid smart card, which clearly shows the antenna connected to the main chip]]

Hybrid cards implement contactless and contact interfaces on a single card with unconnected chips including dedicated modules/storage and processing.

;Dual-interface

Dual-interface cards implement contactless and contact interfaces on a single chip with some shared storage and processing. An example is [[Porto]]'s multi-application transport card, called [[Andante ticket|Andante]], which uses a chip with both contact and [[Contactless smart card|contactless]] (ISO/IEC 14443 Type B) interfaces. Numerous payment cards worldwide are based on hybrid card technology allowing them to communicate in contactless as well as contact modes.

====USB====
The [[CCID (protocol)|CCID]] (Chip Card Interface Device) is a USB protocol that allows a smart card to be interfaced to a computer using a card reader which has a standard USB interface. This allows the smart card to be used as a security token for authentication and data encryption such as [[Bitlocker]]. A typical CCID is a USB dongle and may contain a SIM.

===Logical interfaces===
====Reader side====
Different smart cards implement one or more reader-side protocols. Common protocols here include CT-API and [[PC/SC]].<ref name="kilicli-howto"/>

====Application side====
Smartcard operating systems may provide application programming interfaces (APIs) so that developers can write programs ("applications") to run on the smartcard. Some such APIs, such as [[Java Card]], allow programs to be uploaded to the card without replacing the card's entire operating system.<ref name="kilicli-howto"/>

== Applications ==
=== Financial ===
Smart cards serve as credit or [[ATM card]]s, [[fuel card]]s, mobile phone [[Subscriber Identity Module|SIM]]s, authorization cards for pay television, household utility pre-payment cards, high-security identification and [[access badge]]s, and public transport and public phone payment cards.

Smart cards may also be used as [[electronic wallet]]s. The smart card chip can be "loaded" with funds to pay parking meters, vending machines or merchants. [[Cryptographic protocol]]s protect the exchange of money between the smart card and the machine. No connection to a bank is needed. The holder of the card may use it even if not the owner. Examples are [[Mondex]] (1993), [[Proton (bank card)|Proton]], [[Geldkarte]], [[Chipknip]] and [[Moneo]]. The German Geldkarte is also used to validate customer age at [[vending machine]]s for cigarettes.

{{Main|Contactless smart card|Near-field communication|Credit card}}

These are the best known payment cards (classic plastic card):
* Visa: Visa Contactless, Quick VSDC, "qVSDC", Visa Wave, MSD, payWave
* Mastercard: PayPass Magstripe, PayPass MChip
* American Express: ExpressPay
* Discover: Zip
* Unionpay: QuickPass

Roll-outs started in 2005 in the U.S. Asia and Europe followed in 2006. Contactless (non-PIN) transactions cover a payment range of ~$5–50. There is an [[ISO/IEC 14443]] PayPass implementation. Some, but not all, PayPass implementations conform to EMV.

Non-EMV cards work like [[magnetic stripe card]]s. This is common in the U.S. (PayPass Magstripe and Visa MSD). The cards do not hold or maintain the account balance. All payment passes without a PIN, usually in off-line mode. The security of such a transaction is no greater than with a magnetic stripe card transaction.{{Citation needed|date=October 2015}}

EMV cards can have either contact or contactless interfaces. They work as if they were a normal EMV card with a contact interface. Via the contactless interface they work somewhat differently, in that the card commands enabled improved features such as lower power and shorter transaction times. EMV standards include provisions for contact and contactless communications. Typically modern payment cards are based on hybrid card technology and support both contact and contactless communication modes.

=== SIM ===
The [[subscriber identity module]]s used in mobile-phone systems are reduced-size smart cards, using otherwise identical technologies.

=== Identification ===
Smart-cards can [[authenticate]] identity. Sometimes they employ a [[public key infrastructure]] (PKI). The card stores an encrypted digital certificate issued from the PKI provider along with other relevant information. Examples include the [[United States Department of Defense|U.S. Department of Defense]] (DoD) [[Common Access Card]] (CAC), and other cards used by other governments for their citizens. If they include biometric identification data, cards can provide superior two- or three-factor authentication.

Smart cards are not always privacy-enhancing, because the subject may carry incriminating information on the card. Contactless smart cards that can be read from within a wallet or even a garment simplify authentication; however, criminals may access data from these cards.

Cryptographic smart cards are often used for [[single sign-on]]. Most advanced smart cards include specialized cryptographic hardware that uses algorithms such as [[RSA (algorithm)|RSA]] and [[Digital Signature Algorithm]] (DSA). Today's cryptographic smart cards generate key pairs on board, to avoid the risk from having more than one copy of the key (since by design there usually isn't a way to extract private keys from a smart card). Such smart cards are mainly used for [[digital signature]]s and secure identification.

The most common way to access cryptographic smart card functions on a computer is to use a vendor-provided [[PKCS11|PKCS#11]] library.{{Citation needed|date=May 2010}} On [[Microsoft Windows]] the [[Cryptographic Service Provider]] (CSP) API is also supported.

The most widely used cryptographic algorithms in smart cards (excluding the GSM so-called "crypto algorithm") are [[Triple DES]] and [[RSA (algorithm)|RSA]]. The key set is usually loaded (DES) or generated (RSA) on the card at the personalization stage.

Some of these smart cards are also made to support the [[National Institute of Standards and Technology]] (NIST) standard for [[Personal Identity Verification]], [[FIPS 201]].

Turkey implemented the first smart card driver's license system in 1987. Turkey had a high level of road accidents and decided to develop and use digital tachograph devices on heavy vehicles, instead of the existing mechanical ones, to reduce speed violations. Since 1987, the professional driver's licenses in Turkey have been issued as smart cards. A professional driver is required to insert his driver's license into a digital tachograph before starting to drive. The tachograph unit records speed violations for each driver and gives a printed report. The driving hours for each driver are also being monitored and reported. In 1990 the European Union conducted a feasibility study through BEVAC Consulting Engineers, titled "Feasibility study with respect to a European electronic drivers license (based on a smart-card) on behalf of Directorate General VII". In this study, chapter seven describes Turkey's experience.

Argentina's Mendoza province began using smart card driver's licenses in 1995. Mendoza also had a high level of road accidents, driving offenses, and a poor record of recovering fines.{{Citation needed|date=September 2011}} Smart licenses hold up-to-date records of driving offenses and unpaid fines. They also store personal information, license type and number, and a photograph. Emergency medical information such as blood type, allergies, and biometrics (fingerprints) can be stored on the chip if the card holder wishes. The Argentina government anticipates that this system will help to collect more than $10 million per year in fines.

In 1999 [[Gujarat]] was the first Indian state to introduce a smart card license system.<ref>{{Cite web |url=http://www.parivahan.nic.in/ |title=Smart Card License System |access-date=29 May 2006 |archive-date=10 April 2009 |archive-url=https://web.archive.org/web/20090410042404/http://parivahan.nic.in/ |url-status=dead }}</ref> As of 2005, it has issued 5 million smart card driving licenses to its people.<ref>{{Cite journal |url=https://ideas.repec.org/p/wpa/wuwpur/0510003.html |title="Smart Card Driving License System in Gujarat" |journal=Urban/Regional |date=26 October 2005 |access-date=29 October 2015 |archive-date=4 March 2016 |archive-url=https://web.archive.org/web/20160304131820/https://ideas.repec.org/p/wpa/wuwpur/0510003.html |url-status=live |last1=Kumar |first1=Deepak }}</ref>

In 2002, the Estonian government started to issue smart cards named [[Estonian ID card|ID Kaart]] as primary identification for citizens to replace the usual passport in domestic and EU use. As of 2010 about 1 million smart cards have been issued (total population is about 1.3 million) and they are widely used in internet banking, buying public transport tickets, authorization on various websites etc.

By the start of 2009, the entire population of Belgium was issued eID cards that are used for identification. These cards contain two certificates: one for authentication and one for signature. This signature is legally enforceable. More and more services in Belgium use eID for [[authorization]].<ref>{{cite web |url=http://eid.belgium.be/ |title=Taalkeuze/Choix de langue fedict.belgium.be |publisher=Eid.belgium.be |access-date=13 February 2014 |archive-date=8 February 2014 |archive-url=https://web.archive.org/web/20140208214121/http://eid.belgium.be/ |url-status=live }}</ref>

Spain started issuing national ID cards (DNI) in the form of smart cards in 2006 and gradually replaced all the older ones with smart cards. The idea was that many or most bureaucratic acts could be done online but it was a failure because the Administration did not adapt and still mostly requires paper documents and personal presence.<ref>{{cite web |url=http://www.eldiario.es/turing/dni-electronico-dnie_0_179182675.html |title=Diario Turing – Tecnología y sociedad en red |date=25 September 2013 |access-date=25 August 2017 |archive-date=26 August 2017 |archive-url=https://web.archive.org/web/20170826031709/http://www.eldiario.es/turing/dni-electronico-dnie_0_179182675.html |url-status=live }}</ref><ref>{{cite web |url=http://www.ticbeat.com/tecnologias/reportaje-dni-electronico/ |title=¿Qué fue del DNI electrónico? |work=TICbeat |date=26 April 2015 |access-date=25 August 2017 |archive-date=26 August 2017 |archive-url=https://web.archive.org/web/20170826030716/http://www.ticbeat.com/tecnologias/reportaje-dni-electronico/ |url-status=live |last1=Fraga |first1=Alberto Iglesias }}</ref><ref>{{cite web |title=FRACASO DEL DNI ELECTRONICO |website=A las pruebas me remito |date=4 May 2015 |url=http://blogs.elcomercio.es/hispadata/2015/05/04/fracaso-del-dni-electronico/ |language=es |quote=FAILURE OF THE ELECTRONIC ID |ref={{sfnref | A las pruebas me remito | 2015}} |access-date=6 June 2018 |archive-date=5 March 2018 |archive-url=https://web.archive.org/web/20180305145550/http://blogs.elcomercio.es/hispadata/2015/05/04/fracaso-del-dni-electronico/ |url-status=live }}</ref><ref>{{cite web |title=El DNI electrónico ha muerto: ¡larga vida al DNI 3.0! |date=2 October 2013 |language=es |url=https://www.elconfidencial.com/tecnologia/2013-10-02/el-dni-electronico-ha-muerto-larga-vida-al-dni-3-0_35442/ |quote=The electronic DNI has died: long live the DNI 3.0! |access-date=25 August 2017 |archive-date=26 August 2017 |archive-url=https://web.archive.org/web/20170826071906/https://www.elconfidencial.com/tecnologia/2013-10-02/el-dni-electronico-ha-muerto-larga-vida-al-dni-3-0_35442/ |url-status=live }}</ref>

On 14 August 2012, the ID cards in Pakistan were replaced. The Smart Card is a third generation chip-based [[identity document]] that is produced according to international standards and requirements. The card has over 36 physical security features and has the latest{{clarify|date=May 2017}} encryption codes. This smart card replaced the NICOP (the ID card for [[Pakistani diaspora|overseas Pakistani]]).

Smart cards may identify emergency responders and their skills. Cards like these allow first responders to bypass organizational paperwork and focus more time on the emergency resolution. In 2004, The Smart Card Alliance expressed the needs: "to enhance security, increase government efficiency, reduce identity fraud, and protect personal privacy by establishing a mandatory, Government-wide standard for secure and reliable forms of identification".<ref name="Smart card alliance">{{cite web |url=http://www.smartcardalliance.org/pages/publications-emergency-response-official-credentials |title=Emergency Response Official Credentials: An Approach to Attain Trust in Credentials across Multiple Jurisdictions for Disaster Response and Recovery |date=3 January 2011 |access-date=3 January 2011 |archive-date=27 January 2013 |archive-url=https://web.archive.org/web/20130127012958/http://www.smartcardalliance.org/pages/publications-emergency-response-official-credentials |url-status=dead }}</ref> [[emergency response]] personnel can carry these cards to be positively identified in emergency situations. [[WidePoint Corporation]], a smart card provider to [[Federal Emergency Management Agency|FEMA]], produces cards that contain additional personal information, such as medical records and skill sets.

In 2007, the [[Open Mobile Alliance]] (OMA) proposed a new standard defining V1.0 of the Smart Card Web Server (SCWS), an [[HTTP server]] embedded in a SIM card intended for a [[smartphone]] user.<ref name="oma">{{cite web |url=http://www.openmobilealliance.org/comms/pages/OMA_quarterly_2007_vol_2.htm#news1 |title=OMA Newsletter 2007 Volume 2 |access-date=20 March 2012 |archive-date=19 July 2012 |archive-url=https://web.archive.org/web/20120719083228/http://www.openmobilealliance.org/comms/pages/OMA_quarterly_2007_vol_2.htm#news1 |url-status=live }}</ref> The non-profit trade association SIMalliance has been promoting the development and adoption of SCWS. SIMalliance states that SCWS offers end-users a familiar, [[operating system|OS]]-independent, browser-based interface to secure, personal SIM data. As of mid-2010, SIMalliance had not reported widespread industry acceptance of SCWS.<ref name="http://www.simalliance.org/en?t=/documentManager/sfdoc.file.supply&fileID=1279268442341">{{cite web |url=http://www.simalliance.org/en?t=/documentManager/sfdoc.file.supply&fileID=1279268442341 |title=Update from SIMalliance on SCWS |date=30 June 2010 |access-date=20 March 2012 |author=Martin, Christophe |archive-date=1 August 2013 |archive-url=https://web.archive.org/web/20130801073734/http://www.simalliance.org/en?t=/documentManager/sfdoc.file.supply&fileID=1279268442341 |url-status=live }}</ref> The OMA has been maintaining the standard, approving V1.1 of the standard in May 2009, and V1.2 was expected to be approved in October 2012.<ref name="oma2">{{cite web |title=OMA Smart Card Web Server (SCWS) |url=http://www.openmobilealliance.org/comms/pages/oma_2011_ar_scws.html |url-status=dead |archive-url=https://web.archive.org/web/20121101093544/http://www.openmobilealliance.org/comms/pages/oma_2011_ar_scws.html |archive-date=1 November 2012 |access-date=10 June 2021 }}</ref>

Smart cards are also used to identify user accounts on arcade machines.<ref>{{cite web |url=https://my-aime.net/aime/en/p/info/about.html |title=What is "Aime"? |access-date=6 August 2017 |archive-date=20 March 2014 |archive-url=https://web.archive.org/web/20140320011610/https://my-aime.net/aime/en/p/info/about.html |url-status=live }}</ref>

=== Public transit ===
{{main|List of public transport smart cards|Automated fare collection}}
[[File:Locale_RS6_Transperth SmartRider Card.jpg|thumb|right|SmartRider smart card (Transperth)]]
[[File:ICCard Connection en.svg|thumb|Diagram of Japan's IC card systems and their nationwide interoperability acceptance under the [[Nationwide Mutual Usage Service]] (as of March 2024)]]

Smart cards, used as [[transit pass]]es, and [[integrated ticketing]] are used by many public transit operators. Card users may also make small purchases using the cards. Some operators offer points for usage, exchanged at retailers or for other benefits.<ref>{{Cite web |url=http://www.octopus.com.hk/get-your-octopus/en/index.html |title=Octopus Card Benefits |access-date=31 May 2011 |archive-date=21 July 2011 |archive-url=https://web.archive.org/web/20110721085510/http://www.octopus.com.hk/get-your-octopus/en/index.html |url-status=live }}</ref> Examples include Singapore's [[CEPAS]], Malaysia's [[Touch 'n Go]], Ontario's [[Presto card]], Hong Kong's [[Octopus card]], Tokyo's [[Suica]] and [[PASMO]] cards, London's [[Oyster card]], Ireland's [[TFI Leap Card|Leap Card]], Brussels' [[MoBIB]], Québec's [[Opus card]], Boston's [[CharlieCard]], San Francisco's [[Clipper card]], Washington, D.C.'s [[SmarTrip]], Auckland's [[AT HOP card|AT Hop]], Brisbane's [[go card]], Perth's [[SmartRider]], Sydney's [[Opal card]] and Victoria's [[myki]]. However, these present a [[privacy]] risk because they allow the mass transit operator (and the government) to track an individual's movement. In Finland, for example, the Data Protection [[Ombudsman]] prohibited the transport operator [[Helsinki Metropolitan Area Council]] (YTV) from collecting such information, despite YTV's argument that the card owner has the right to a list of trips paid with the card. Earlier, such information was used in the investigation of the [[Myyrmanni bombing]].{{Citation needed|date=May 2011}}

The UK's [[Department for Transport]] mandated smart cards to administer travel entitlements for elderly and disabled residents. These schemes let residents use the cards for more than just bus passes. They can also be used for taxi and other concessionary transport. One example is the "Smartcare go" scheme provided by Ecebs.<ref>{{cite web |url=http://www.ecebs.com/local-government-products/smartcare-go.html |title=Smartcare go |access-date=24 September 2012 |archive-date=9 October 2012 |archive-url=https://web.archive.org/web/20121009060525/http://www.ecebs.com/local-government-products/smartcare-go.html |url-status=live }}</ref> The UK systems use the [[ITSO Ltd]] specification. Other schemes in the UK include period travel passes, carnets of tickets or day passes and stored value which can be used to pay for journeys. Other concessions for school pupils, students and job seekers are also supported. These are mostly based on the [[ITSO Ltd]] specification.

Many smart transport schemes include the use of low cost smart tickets for simple journeys, day passes and visitor passes. Examples include Glasgow [[Glasgow Subway|SPT subway]]. These smart tickets are made of paper or PET which is thinner than a PVC smart card e.g. Confidex smart media.<ref>{{cite web |url=https://www.confidex.com/products/public-transport-ticketing |title=Smart Tickets |access-date=24 April 2018 |archive-date=25 April 2018 |archive-url=https://web.archive.org/web/20180425115302/https://www.confidex.com/products/public-transport-ticketing |url-status=live }}</ref> The smart tickets can be supplied pre-printed and over-printed or printed on demand.

In Sweden, as of 2018–19, the old SL Access smart card system has started to be phased out and replaced by smart [[phone app]]s. The phone apps have less cost, at least for the transit operators who don't need any electronic equipment (the riders provide that). The riders are able buy tickets anywhere and don't need to load money onto smart cards. New NFC smart cards are still in use for foreseeable future (as of 2024).

=== Video games ===

In Japanese [[amusement arcade]]s, [[contactless smart card]]s (usually referred to as "IC cards") are used by game manufacturers as a method for players to access in-game features (both online like [[Konami]] [[E-Amusement]] and [[Sega]] [[ALL.Net]] and offline) and as a memory support to save game progress. Depending on a case by case scenario, the machines can use a game-specific card or a "universal" one usable on multiple machines from the same manufacturer/publisher. Amongst the most widely used there are Banapassport by [[Bandai Namco Entertainment|Bandai Namco]], [[E-amusement pass]] by [[Konami]], Aime by [[Sega]] and [[Nesica]] by [[Taito]].

In 2018, in an effort to make arcade game IC cards more user friendly,<ref>{{Cite web |url=https://www.konami.com/amusement/corporate/en/news/release/20180209/ |title=Konami Amusement, Sega Interactive, and Bandai Namco Entertainment Agree on Unified System for Arcade Game IC Cards |access-date=10 June 2020 |archive-date=10 June 2020 |archive-url=https://web.archive.org/web/20200610084912/https://www.konami.com/amusement/corporate/en/news/release/20180209/ |url-status=live }}</ref> Konami, Bandai Namco and Sega have agreed on a unified system of cards named ''Amusement IC''. Thanks to this agreement, the three companies are now using a unified card reader in their arcade cabinets, so that players are able to use their card, no matter if a Banapassport, an e-Amusement Pass or an Aime, with hardware and ID services of all three manufacturers. A common logo for ''Amusement IC'' cards has been created, and this is now displayed on compatible cards from all three companies. In January 2019, Taito announced<ref>{{Cite web |url=https://game.watch.impress.co.jp/docs/news/1165709.html |title=タイトー、「アミューズメントICカード」規格に参入決定。タイトー対応タイトル第1弾は「ストV タイプアーケード」 |date=22 January 2019 |access-date=10 June 2020 |archive-date=10 June 2020 |archive-url=https://web.archive.org/web/20200610084911/https://game.watch.impress.co.jp/docs/news/1165709.html |url-status=live }}</ref> that their Nesica card was also joining the ''Amusement IC'' agreement with the other three companies.

=== Computer security ===
Smart cards can be used as a [[security token]].

[[Mozilla Foundation|Mozilla's]] [[Firefox]] [[web browser]] can use smart cards to store [[Public key certificate|certificate]]s for use in secure web browsing.<ref>[//www.mozilla.org/projects/security/pki/pkcs11/ Mozilla certificate store]</ref>

Some [[Disk encryption software|disk encryption systems]], such as [[VeraCrypt]] and Microsoft's [[BitLocker]], can use smart cards to securely hold encryption keys, and also to add another layer of encryption to critical parts of the secured disk.

[[GNU Privacy Guard|GnuPG]], the well known encryption suite, also supports storing keys in a smart card.<ref>[http://www.gnupg.org/documentation/howtos.en.html#GnuPG-cardHOWTO smartcard] {{Webarchive|url=https://web.archive.org/web/20120917080846/http://www.gnupg.org/documentation/howtos.en.html#GnuPG-cardHOWTO |date=17 September 2012 }} howto for GNUPG</ref>

Smart cards are also used for [[single sign-on]] to [[log on]] to computers.

=== Schools ===
Smart cards are being provided to students at some schools and colleges.<ref>{{cite news |url=http://www.theage.com.au/news/Breaking/Qld-schools-benefit-from-smart-cards/2004/12/06/1102182194085.html?from=moreStories |work=The Age |first=Sam |last=Varghese |title=Qld schools benefit from smart cards |date=6 December 2004 |access-date=20 May 2011 |archive-date=6 November 2012 |archive-url=https://web.archive.org/web/20121106204136/http://www.theage.com.au/news/Breaking/Qld-schools-benefit-from-smart-cards/2004/12/06/1102182194085.html?from=moreStories |url-status=live }}</ref><ref>{{cite web |author=CreditCards.com |url=http://australia.creditcards.com/credit-card-news/cashless-lunches-come-to-australian-schools.php |archive-url=https://web.archive.org/web/20101129142951/http://australia.creditcards.com/credit-card-news/cashless-lunches-come-to-australian-schools.php |url-status=dead |archive-date=29 November 2010 |title=Cashless lunches come to Australian schools |publisher=Australia.creditcards.com |date=27 October 2009 |access-date=13 February 2014 }}</ref><ref>{{cite web |url=http://www.ifr.ac.uk/media/newsreleases/smartcard.html |archive-url=https://web.archive.org/web/20051120144245/http://www.ifr.ac.uk/Media/NewsReleases/smartcard.html |url-status=dead |archive-date=20 November 2005 |title=News Release – Smart card technology to monitor smart food choices in schools |publisher=Ifr.ac.uk |date=14 July 2005 |access-date=13 February 2014 }}</ref> Uses include:

* Tracking student attendance
* As an [[electronic purse]], to pay for items at canteens, vending machines, laundry facilities, etc.
* Tracking and monitoring food choices at the canteen, to help the student maintain a healthy diet
* Tracking loans from the school library
* [[Access control]] for admittance to restricted buildings, [[dormitories]], and other facilities. This requirement may be enforced at all times (such as for a laboratory containing valuable equipment), or just during after-hours periods (such as for an academic building that is open during class times, but restricted to authorized personnel at night), depending on security needs.
* Access to transportation services

=== Healthcare ===
{{further|eHealth|health informatics|electronic health record}}
Smart health cards can improve the [[data security|security]] and [[medical privacy|privacy]] of patient information, provide a secure carrier for portable [[medical record]]s, reduce [[health care fraud]], support new processes for portable medical records, provide secure access to emergency medical information, enable compliance with government initiatives (e.g., [[organ donation]]) and mandates, and provide the platform to implement other applications as needed by the [[health care organization]].<ref>{{Cite web |url=http://www.smartcardalliance.org/pages/smart-cards-applications-healthcare |title=Smartcardalliance.org |access-date=10 March 2009 |archive-date=25 March 2009 |archive-url=https://web.archive.org/web/20090325055054/http://www.smartcardalliance.org/pages/smart-cards-applications-healthcare |url-status=live }}</ref><ref name=fernandez2013>{{cite journal |last1=Fernández-Alemán |first1=José Luis |last2=Señor |first2=Inmaculada Carrión |last3=Lozoya |first3=Pedro Ángel Oliver |last4=Toval |first4=Ambrosio |title=Security and privacy in electronic health records: A systematic literature review |journal=Journal of Biomedical Informatics |publisher=Elsevier BV |volume=46 |issue=3 |year=2013 |issn=1532-0464 |doi=10.1016/j.jbi.2012.12.003 |pmid=23305810 |pages=541–562 |quote=Recent years have witnessed the design of standards and the promulgation of directives concerning security and privacy in EHR systems. However, more work should be done to adopt these regulations and to deploy secure EHR systems. |doi-access=free }}</ref>

=== Other uses ===
Smart cards are widely used to [[television encryption|encrypt]] digital television streams. [[VideoGuard]] is a specific example of how smart card security worked.

=== Multiple-use systems ===
The Malaysian government promotes [[MyKad]] as a single system for all smart-card applications. MyKad started as identity cards carried by all citizens and resident non-citizens. Available applications now include identity, travel documents, drivers license, health information, an electronic wallet, ATM bank-card, public toll-road and transit payments, and public key encryption infrastructure. The personal information inside the MYKAD card can be read using special APDU commands.<ref>[https://web.archive.org/web/20080123113825/http://mykadpro.net/ MYKAD SDK]</ref>

== Security ==
{{more citations needed section|date=February 2016}}
Smart cards have been advertised as suitable for personal identification tasks, because they are [[security engineering|engineered]] to be [[tamper resistant]]. The chip usually implements some [[cryptography|cryptographic]] algorithm. There are, however, several methods for recovering some of the algorithm's internal state.

[[Differential power analysis]] involves measuring the precise time and [[electric current]] required for certain encryption or decryption operations. This can deduce the on-chip private key used by public key algorithms such as [[RSA (algorithm)|RSA]]. Some implementations of [[symmetric cipher]]s can be vulnerable to timing or [[power analysis|power attacks]] as well.

Smart cards can be physically disassembled by using acid, abrasives, solvents, or some other technique to obtain unrestricted access to the on-board microprocessor. Although such techniques may involve a risk of permanent damage to the chip, they permit much more detailed information (e.g., [[photomicrograph]]s of encryption hardware) to be extracted.

==Advantages==

The primary advantage of smart cards is their flexibility. Smart cards have multiple functions which simultaneously can be an ID, a credit card, a stored-value cash card, and a repository of personal information such as telephone numbers or medical history. The card can be easily replaced if lost, and, the requirement for a [[Personal identification number|PIN]] (or other form of security) provides additional security from unauthorised access to information by others. At the first attempt to use it illegally, the card would be deactivated by the card reader itself.

The secondary advantage is security. Smart cards can be electronic key rings, giving the bearer ability to access information and physical places without need for online connections. They are encryption devices, so that the user can encrypt and decrypt information without relying on unknown, and therefore potentially untrustworthy, appliances such as ATMs. Smart cards are very flexible in providing authentication at different level of the bearer and the counterpart. Finally, with the information about the user that smart cards can provide to the other parties, they are useful devices for customizing products and services. Smart cards can also have multiple credentials for different applications. This encourages better security as the user only has to manage a single card which is not only less cognitive load and more convenient.

The tertiary advantage is reduced cost. Smart cards are easily produced and have vastly improved security allowing institutions to reduce their security spending.

Other general benefits of smart cards are:

*Portability
*Increasing [[data storage]] capacity
*Reliability that is virtually unaffected by electrical and magnetic fields.

==Smart cards and electronic commerce==
Smart cards can be used in [[electronic commerce]], over the Internet, though the business model used in current electronic commerce applications still cannot use the full feature set of the electronic medium. An advantage of smart cards for electronic commerce is their use customize services. For example, for the service supplier to deliver the customized service, the user may need to provide each supplier with their profile, a boring and time-consuming activity. A smart card can contain a non-encrypted profile of the bearer, so that the user can get customized services even without previous contacts with the supplier.

== Disadvantages ==
[[File:Locale_RS6_Carteapuce.jpg|thumb|right|upright|A false smart card, with two 8-bit [[CMOS]] [[microcontroller]]s, used in the 1990s to decode the signals of Sky Television]]

The plastic or paper card in which the chip is embedded is fairly flexible. The larger the chip, the higher the probability that normal use could damage it. Cards are often carried in wallets or pockets, a harsh environment for a chip and antenna in contactless cards. PVC cards can crack or break if bent/flexed excessively. However, for large banking systems, failure-management costs can be more than offset by fraud reduction.{{citation needed|date=February 2013}}

The production, use and disposal of PVC plastic is known to be more harmful to the environment than other plastics.<ref>{{cite web |url=https://www.greenpeace.org/usa/toxics/pvc-free/ |title=PVC free |date=29 June 2015 |publisher=Greepeace |access-date=24 April 2018 |archive-date=25 April 2018 |archive-url=https://web.archive.org/web/20180425115447/https://www.greenpeace.org/usa/toxics/pvc-free/ |url-status=live }}</ref> Alternative materials including chlorine free plastics and paper are available for some smart applications.

If the account holder's computer hosts [[malware]], the smart card security model may be broken. Malware can override the communication (both input via keyboard and output via application screen) between the user and the application. [[Man-in-the-browser]] malware (e.g., the Trojan [[Silentbanker]]) could modify a transaction, unnoticed by the user. Banks like [[Fortis (finance)|Fortis]] and [[Belfius]] in Belgium and [[Rabobank]] ("[[:nl:Random Reader|random reader]]") in the Netherlands combine a smart card with an unconnected card reader to avoid this problem. The customer enters a challenge received from the bank's website, a PIN and the transaction amount into the reader. The reader returns an 8-digit signature. This signature is manually entered into the personal computer and verified by the bank, preventing [[Point-of-sale malware|point-of-sale-malware]] from changing the transaction amount.

Smart cards have also been the targets of security attacks. These attacks range from physical invasion of the card's electronics, to non-invasive attacks that exploit weaknesses in the card's software or hardware. The usual goal is to expose private encryption keys and then read and manipulate secure data such as funds. Once an attacker develops a non-invasive attack for a particular smart card model, he or she is typically able to perform the attack on other cards of that model in seconds, often using equipment that can be disguised as a normal smart card reader.<ref>{{cite web |url=http://www.infosecwriters.com/text_resources/pdf/Known_Attacks_Against_Smartcards.pdf |title=Known Attacks Against Smartcards |publisher=Discretix Technologies Ltd |access-date=20 February 2013 |author=Bar-El, Hagai |archive-date=12 May 2013 |archive-url=https://web.archive.org/web/20130512100956/http://www.infosecwriters.com/text_resources/pdf/Known_Attacks_Against_Smartcards.pdf |url-status=live }}</ref> While manufacturers may develop new card models with additional [[information security]], it may be costly or inconvenient for users to upgrade vulnerable systems. [[Tamper-evident]] and audit features in a smart card system help manage the risks of compromised cards.

Another problem is the lack of standards for functionality and security. To address this problem, the Berlin Group launched the ERIDANE Project to propose "a new functional and security framework for smart-card based Point of Interaction (POI) equipment".<ref>{{cite web |url=http://www.berlin-group.org/related-eridane.html |archive-url=https://web.archive.org/web/20060507222917/http://www.berlin-group.org/related-eridane.html |url-status=dead |archive-date=7 May 2006 |title=Related Initiatives |access-date=20 December 2007 |date=1 August 2005 |work=Home web for The Berlin Group |publisher=[[The Berlin Group]] }}</ref>

==See also==
{{Div col}}
* [[Campus card]]
* [[Java Card]]
* [[Keycard lock]]
* [[List of public transport smart cards]]
* [[Multi-factor authentication]]
* [[MULTOS]]
* [[Open Smart Card Development Platform]]
* [[Payment Card Industry Data Security Standard]]
* [[Proximity card]]
* [[Radio-frequency identification]]
* [[SNAPI]]
* [[Smart card application protocol data unit|Smart card application protocol data unit (APDU)]]
* [[Smart card management system]]
{{div col end}}

== References ==
{{Reflist|30em}}

== Further reading ==
{{refbegin}}
* {{ cite book |first=W. |last=Rankl |author2=W. Effing |title=Smart Card Handbook |publisher=John Wiley & Sons |year=1997 |isbn=0-471-96720-3}}
* {{cite book |first=Scott B. |last=Guthery |author2=Timothy M. Jurgensen |title=SmartCard Developer's Kit |publisher=Macmillan Technical Publishing |year=1998 |isbn=1-57870-027-2 |url-access=registration |url=https://archive.org/details/smartcarddevelop00guth}}
{{refend}}

== External links ==
{{commons category|Smart cards|position=}}

{{Credit cards}}
{{Chinese smartcards}}
{{Japanese smartcards}}
{{American smartcards}}
{{Broadcast encryption}}
{{Authority control}}

[[Category:Smart cards| ]]
[[Category:Banking technology]]
[[Category:German inventions]]
[[Category:ISO standards]]
[[Category:Ubiquitous computing]]
[[Category:Authentication methods]]

File:Locale RS6 Transperth SmartRider Card.jpg

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RS-485: Imported from Wikipedia

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File:Locale RS6 New Finnish ID card (front side).jpg

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File:Locale RS6 Differentsmartcardpadlayouts.jpg

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RS-485: Imported from Wikipedia

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File:Locale RS6 Carteapuce.jpg

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File:Locale RS6 Australia Bank Paypass Card.png

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File:Locale RS6 1979 erste G&D-Chipkarte (8 Kontakte).jpg

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Simplex communication

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RS-485: Imported from Wikipedia (overwrite)

#REDIRECT [[Duplex (telecommunications)#Simplex]]

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[[Category:Communication circuits]]

Signetics 2650

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RS-485: Imported from Wikipedia (overwrite)

{{short description|8-bit microprocessor}}
{{Infobox CPU
|name = Signetics 2650
|image = KL Signetics 2650AN.jpg
|caption = Signetics 2650AN
|produced-start = {{Start date and age|1975}}
|produced-end =
|slowest = 1.2 | slow-unit = MHz
|fastest =
|manuf1 = [[Signetics]], [[Philips]]
|arch =
|transistors =
|instructions =
|data-width = 8
|address-width = 15
|pack1 = 40-pin [[Dual in-line package|DIP]]
}}

The '''Signetics 2650''' was an [[8-bit]] [[microprocessor]] introduced in July 1975.<ref>{{Cite web |url=http://bitsavers.trailing-edge.com/pdf/microcomputerAssociates/Microcomputer_Digest_v02n01_Jul75.pdf |title=Microcomputer Digest Vol. 2 No. 1 July 1975 |access-date=1 February 2014 |archive-url=https://web.archive.org/web/20140201234414/http://bitsavers.trailing-edge.com/pdf/microcomputerAssociates/Microcomputer_Digest_v02n01_Jul75.pdf |archive-date=1 February 2014 |url-status=live }}</ref> According to [[Adam Osborne]]'s book ''An Introduction to Microprocessors Vol 2: Some Real Products'', it was "the most [[minicomputer]]-like" of the microprocessors available at the time. A combination of missing features and odd memory access limited its appeal, and the system saw little use in the market.

==Development==
[[File:Locale_RS6_Signetics 2650 microprocessor October 1975.jpg|thumb|300px|right|Signetics 2650 introductory ad, October 30, 1975]]

In 1972, Signetics' Jack Curtis{{efn|Best known for his joke article on [[Write-only_memory_(joke)|write-only memory]].}} hired John Kessler of [[IBM]] to lead the design of a new single-chip CPU intended to compete with [[minicomputer]] systems. Kessler selected the [[IBM 1130]] as the model for the new design. The 1130, released in 1965, was a [[16-bit]] [[minicomputer]] that shared many design features with other minis of the era.<ref name=shack/>

While Kessler designed the architecture, Kent Andreas laid out the CPU using a recently developed [[ion implantation]] [[NMOS logic|NMOS]] process. In contrast to the far more common [[PMOS logic|PMOS]] process of the era, NMOS used less power and dissipated less heat. This allowed the chip to be run at higher speeds than PMOS CPU designs, and the first 2650's ran at the same 1.25 MHz speed as the contemporary models of the 1130.<ref name=shack/>

When it was designed in 1972, the 2650 was among the most advanced designs on the market, easily outperforming and out-featuring the [[Intel 4004]] and [[Intel 8008|8008]] of the same era. Despite this, the design was not released to production. At the time, Signetics was heavily involved with [[Dolby Laboratories]], developing [[integrated circuit]]s that implemented Dolby's suite of [[Dolby noise-reduction system|noise-reduction system]]s. Production of the 2650 was pushed back, and the CPU was not formally introduced until July 1975. By 1975, several new CPUs had been introduced, designed from the start to be 8-bit machines rather than mimicking an older design, and the 2650's advantages were no longer as compelling.<ref name=shack/>

In 1975, [[Philips]] purchased Signetics, and from that point versions of the 2650 can be found with both Signetics or Philips branding.<ref name=shack/>

In March 1976, Signetics reached a second-source agreement with [[Advanced Memory Systems]] (AMS). At that time, most CPU firms were very small and no one would buy a design from a company that might go bankrupt. Second-sourcing was an important guarantee that the design would remain available in this eventuality. AMS was already acting as a second-source for the [[RCA 1802]], an advanced [[CMOS]] design. The NMOS 2650 was seen as a useful adjunct that would not directly compete with the 1802. Unfortunately, in November AMS was purchased by [[Intersil]], who had their own [[Intersil 6100]], a single-chip version of the [[PDP-8]] mini. Intersil dropped production of the 2650.<ref name=shack/>

Signetics tried again with [[National Semiconductor]] in 1977, who planned to introduce versions in the last quarter of the year. For unknown reasons, this appears to have never happened, and only a single example of an NS version, from France, has ever been found.<ref name=shack/>

Signetics continued the development of the 2650, introducing two new models in 1977. The 2650A was a reworked version of the original layout intended to improve yield, and thus reduce cost. Speed remained unchanged at 1.25 MHz for the base model and 2 MHz for the -1 versions. The 2650B was based on the A, added two new instructions, and improved the performance of a number of existing instructions.<ref name=shack/>

==Description==
[[File:Locale_RS6_Signetics 2650A die.JPG|thumb|right|Signetics 2650A chip magnified.]]

{| class="infobox" style="font-size:88%;width:31em;"
|+ Signetics 2650 registers
|-
| style="text-align:center;"| 14
| style="text-align:center;"| 13
| style="text-align:center;"| 12
| style="text-align:center;"| 11
| style="text-align:center;"| 10
| style="text-align:center;"| 09
| style="text-align:center;"| 08
| style="text-align:center;"| 07
| style="text-align:center;"| 06
| style="text-align:center;"| 05
| style="text-align:center;"| 04
| style="text-align:center;"| 03
| style="text-align:center;"| 02
| style="text-align:center;"| 01
| style="text-align:center;"| 00
| ''(bit position)''
|-
|colspan="16" | '''Main general purpose registers''' 
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="8"| REG0
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="8"| REG1
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="8"| REG2
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="8"| REG3
|-
|colspan="16" | '''Alternate general purpose registers''' 
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="8"| REG1'
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="8"| REG2'
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="8"| REG3'
|-
|colspan="16" | '''Instruction Address register''' 
|- style="background:silver;color:black"
| style="text-align:center;" colspan="2"| Page
| style="text-align:center;" colspan="13"|
|-
|colspan="16" | '''Subroutine return address stack''' 
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S0
|-
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S1
|-
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S2
|-
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S2
|-
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S4
|-
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S5
|-
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S6
|-
|- style="background:silver;color:black"
| style="text-align:center;" colspan="15"| S7
|-
|colspan="16" | '''Program Status Words'''
|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;"| S
| style="text-align:center;"| F
| style="text-align:center;"| II
| style="text-align:center;" colspan="2"|
| style="text-align:center;" colspan="3"| Stack Ptr
| style="background:white; color:black" | PSU

|- style="background:silver;color:black"
| style="text-align:center; background:white" colspan="7" |  
| style="text-align:center;" colspan="2"| CC
| style="text-align:center;"| ID
| style="text-align:center;"| RS
| style="text-align:center;"| WC
| style="text-align:center;"| OV
| style="text-align:center;"| CM
| style="text-align:center;"| C
| style="background:white; color:black" | PSL
|}

The overall design of the 2650 was based on the [[IBM 1130]]. As such, the 2650 has a number of features that were common on 1960s [[minicomputer]]s, but rarely found on newly designed microprocessors of the 1970s. Among these, for instance, were processor status bits that were used to track the status of [[input/output]] devices, which makes it simpler to write interfacing code.<ref name=shack>{{cite web |title=Signetics 2650: An IBM on a Chip |website=CPU Shack |date=16 October 2016 |url=http://www.cpushack.com/2016/10/16/signetics-2650-an-ibm-on-a-chip/}}</ref> Another mini-like feature was its use of [[vectored interrupt]]s, which allowed devices to call the correct [[interrupt handler]] code by putting its memory location on the data bus and then forcing an interrupt. This avoids the need to write a centralized interrupt handler that reads additional data from the bus, determines which [[device driver]] is being invoked and then calls it; the 2650 can jump directly to the correct code, potentially stored on the device itself.

The 2650's [[processor register]]s were divided into sets, with a single global register R0 used as the [[Accumulator (computing)|accumulator]], and two sets of three [[index register]]s, both named R1, R2 and R3, for a total of seven registers.{{sfn|Rowe|1976}} For clarity, the second set was sometimes referred to as R1', R2' and R3' ("prime"). At any one time, one of the two sets of indexes were visible to the CPU. Which set was visible was controlled by a bit in the [[status register]], PSW. One could easily switch between the two sets of registers with a single instruction.<ref name=world>{{cite web |website=CPU World |title= Signetics 2650 family |url=https://www.cpu-world.com/CPUs/2650/index.html |date=11 February 2014 }}</ref> This allowed rapid switching of values during subroutine calls, [[operating system]] switches, or handling interrupts. Unlike the 1130, the registers were only 8-bit wide rather than 16-bit, but there were two sets in the 2650 rather than one in the 1130.<ref name=shack/>

Another of its mini-like features was the extensive support for [[indirect addressing]] on most instructions. Many instructions require data to be read from a location in memory, in most CPUs of the era that would be a single byte of data that is stored in memory referred to by a 16-bit location. In the 2650, the high-bit of that 16-bit location indicated indirection, meaning that the data was not located at this location in memory, but the one encoded in the remaining 15 bits of the address.<ref name=world/> This style of access allowed blocks of data to be more easily accessed than in systems that provided indirection solely through special instructions or index registers. One could step through memory by incrementing the address value stored in that single location in memory. This also resulted in considerable numbers of math instructions being applied to addresses, and to improve the performance of these operations, the 2650 included a second [[arithmetic logic unit]] just for address calculations.{{sfn|Rowe|1976}}

The downside to this approach was that the high-bit was no longer part of the address, meaning the [[address space]] was only 15 bits, and the machine could access only a total of 32 KB of memory. The address space was further limited by the use of another two bits of the address to indicate the indexing mode for all logical and arithmetic (i.e. non-branch) instructions. These bits controlled functions like whether the address should be post-incremented or pre-decremented, which is extremely useful for constructing loops. But with all of these bits already accounted for, only 13 were available for addresses in these instructions, meaning only 8 KB could be addressed directly. This meant the main memory was broken up as four 8 KB blocks.{{sfn|Rowe|1976}} To access memory outside the 8 KB where the instruction was located, the data bytes being pointed to had to contain an indirect address, pointing to some other location in memory.<ref name=world/> Doing so forced another memory read cycle, slowing performance.

When the 2650 was designed in 1972, these limitations on address space were not significant due to the small size and high cost of the [[static RAM]] memory typically used with these processors. At the time, machines typically contained 2 or 4 KB of RAM. But with the increasing use of [[dynamic RAM]] from the mid-1970s, machines with 8 and 16 KB of RAM, and ultimately 64 KB, became common and the addressing system on the 2650 became a significant hindrance.

The 2650 also contained an on-die [[call stack]], rather than the more common solution that sets aside a location in memory to hold the stack. The [[stack pointer]] was held in three bits in the PSW. An on-die stack is much faster, as the data can be accessed directly without waiting for it to be read from external memory, but it also takes up room on the die and is always limited in size as a result of practical tradeoffs. In the 2650, the return address stack was eight 15-bit entries deep.{{sfn|Rowe|1976}} This allowed programs to nest subroutines to eight levels.

While there were nine different [[addressing mode]]s, the lack of 16-bit registers and the 13–15-bit address space prevented widespread use. Despite this, an [[operating system]] ("2650 DOS")<ref>[https://ztpe.nl/2650/software/disk-operating-system/ 2650 DOS]</ref> was available, along with 8 KB and 12 KB [[BASIC]] interpreters (sold by Central Data Corporation USA), and many games of the ''[[Hunt the Wumpus]]'' style. Most programs were written in [[assembly language]].

==Uses==
[[File:Locale_RS6_Signetics PC1001.jpg|thumb|right|PC1001 evaluation board]]

Signetics sold 2650-based [[microprocessor development board]]s, first the PC1001<ref>Signetics Technical Note SP50; 2650 evaluation printed circuit board level system PC1001</ref><ref>Signetics Technical Note SS50; PC1001 monitor program "PIPBUG"</ref> and then its successor, the PC1500 "Adaptable Board Computer", ranging in price from A$165 to A$400. The chip by itself sold for around A$20. Several hardware construction projects and programming articles were published in magazines such as ''[[Electronics Australia]]'' and ''[[Elektor]]'' and related kits were sold by electronics stores. These factors led to its use by a number of [[hobby]]ists in many countries such as Australia, U.S.A.,<ref>Build a 2650 Microcomputer system, Radio Electronics magazine: April, May, June 1977</ref> United Kingdom, the Netherlands<ref>[[Hobby Computer Club]] (HCC) 2650 user group</ref> and Germany.<ref>Programmierbeispiele mit dem Mikroprozessor 2650, Johann Hatzenbichler, 1978 {{oclc|74475572}}</ref>

Two types of [[video game console]] used the Signetics 2650 or 2650A. The first group of consoles are based on the [[Signetics 2636]] [[video display controller]]; the [[Interton Video Computer 4000]] (1978) and variants of the [[1292 Advanced Programmable Video System]] (1979) belong to this group. The second group of consoles were based on the [[Signetics 2637]] as a [[video display controller]]; [[Emerson Radio|Emerson]] [[Arcadia 2001]] which was released in 1982 and which used a Signetics 2650 running at 0.895 [[Hertz|MHz]] as a [[Central processing unit|CPU]] belong to this group together with many other ones software-compatible (Leonardo, [[Hanimex]] MPT-03 etc.).<ref>{{cite web |url=https://www.digitpress.com/the_digs/arcadia/texts/2001-faq.htm#warning |title=Arcadia 2001: Frequently Asked Questions |date=4 June 2002 |access-date=26 December 2023 |first=Ward |last=Sharke |display-authors=etal |others=See "Credits and contributions" section for authors.}}</ref>

[[File:Locale_RS6_Photo Aug 31, 10 32 33 PM.jpg|thumb|Signetics 2650 Microprocessor Kit]]

At least six coin-operated video games were released in the 1970s which used the 2650 CPU: [[Atari, Inc.|Atari's]] ''[[Quiz Show (video game)|Quiz Show]]'', Meadows Games ''3D Bowling'', ''Gypsy Juggler'' and ''Lazer Command'', [[Cinematronics]] ''Embargo'', and a 1978 clone of ''[[Space Invaders]]'' by Italian company [[Zaccaria (company)|Zaccaria]] called ''The Invaders'' (the original by [[Taito]] uses an [[Intel 8080]] CPU). At least two coin-operated video games were released in the 1980s using the 2650. ''[[Hunchback (video game)|Hunchback]]'', and ''[[Hunchback Olympic]]''.

Zaccaria also released 28 pinball machines based on the 2650 CPU. Their successor company, MrGame, released four additional pinball machines using the 2650. Zaccaria seems to have licensed its design to Technoplay as well, and several more pinball machines were released using variations of Zaccaria circuit board designs.

The processor was also used in the [[Signetics Instructor 50]], which was a small computer designed to teach the use and programming of the 2650 CPU.

The 2650 was also used in some large items of equipment such as the Tektronix 8540, a microprocessor software development system which supported various [[in-circuit emulator]], trace memory and logic analyser cards for real-time debugging of microprocessor systems, as practiced in the 1980s. The 2650 provided the base operating system functions, data transfer, and interface to a host computer or serial computer terminal.

The processor was most suited as a microcontroller, due to its extensive I/O support:

* Single bit i/o pins on the processor (sense/flag bits)
* Signals to directly address two 8-bit I/O ports (control and data ports) using single byte instructions ([[Port I/O|port i/o]]). This circumvented the elaborate hardware other systems needed for [[memory-mapped I/O]]
* Signals to address another 256 I/O ports using an 8-bit address and two byte instructions, again, limiting the amount of hardware (address decoding) required. Philips emphasized this use as a micro-controller with a demonstration program showing the 2650 controlling an intelligent elevator system. Also, at trade fairs they showed the 2650 controlling a miniature 'sort and stack' robot

==Industrial Microcomputer System – IMS==
[[File:Locale_RS6_IMS001b.jpg|thumb|Philips IMS 2650 Eurocard computer system]]
For a short time starting 1979, Philips sold a modular 2650 computer called the 'IMS'{{snd}} Industrial Microcomputer System,<ref>Industrial Microcomputer System; System Specification, Philips Electronic Components and materials, 1980</ref> based on the [[Eurocard (printed circuit board)|Eurocard]] format in a 19" rack. It included [[CPU]], PROM, [[Random-access memory|RAM]], input, output and teletype modules. This system was meant as a more intelligent [[programmable logic controller]]. For development, they later added DEBUG, DISPLAY, INTERRUPT and MODEST ((E)PROM programmer) modules.

==Architecture==
The 2650 was supplied in a 40 pin plastic or ceramic [[Dual in-line package|DIL]] enclosure. An external single phase clock signal and a single 5V supply were needed.

The 2650 had many unusual features when compared to other microprocessors of the time:

*It was a fully static NMOS 8-bit microprocessor. The static nature was unusual for the time, and meant that the processor could be halted simply by stopping the clock signal. Programmers made grateful use of this feature to "single step' through a program using a push-button switch to generate the clock pulses.
*Unique was the 8-level 15-bit wide stack for the subroutine and interrupt return addresses which was integrated into the processor. The stack pointer used 3 bits of the upper status register. This meant subroutines and interrupts could only be nested 8 levels deep.
*The processor had only 13 real address lines, a further 2 address lines were connected to a 2-bit 'page register', resulting in a 32 KB address space. The page register was set when an absolute (direct) branch instruction, which used a full 15-bit address, was executed. All logical and arithmetic instructions used a 13-bit address augmented by the contents of the page register, thereby limiting their scope to an 8 KB page. These 2 upper address lines were also used (multiplexed) to select the appropriate I/O port during I/O operations (Control port, Data port or Extended port).
*Although the 2650 had only one interrupt input, this was a 'vectored' interrupt – the interrupting device needed to put a zero-relative displacement on the data bus, that would be used as the operand of a ZBSR (zero branch to subroutine relative) instruction to branch to the specified interrupt routine. Therefore, using indirect addressing, a maximum of 30 interrupt vectors could be stored in the first 64 bytes of memory. (The first three bytes were needed to hold an unconditional branch to the 'reset' routine). This vectored interrupt is also reminiscent of the [[PDP-11]] [[minicomputer]].

==Instruction set==
Although the 2650 is basically an 8-bit microprocessor, up to three bits of the addresses were also used with the 8-bit instruction to form longer opcodes. 64 opcodes are 9-bits long, and another 32 opcodes are 11-bit. Of the remaining 128 8-bit opcodes, 124 (126 in the 2650B) are implemented, giving a total of 444 (446) instructions.

Many more instructions are available as the behavior of the standard instructions can be modified by setting or clearing status bits: WC (with or without carry) and COM (logical or arithmetic compare). This doubled the number of rotate, add, subtract and compare instructions.

The instruction set is strongly [[orthogonal instruction set|orthogonal]]: all logic and arithmetic instructions can use all nine addressing modes:

* register
* immediate
* PC relative and PC relative indirect
* absolute and absolute indirect
* absolute indexed, absolute indexed with auto-increment, and absolute indexed with auto-decrement, both direct and indirect

The most significant bit of all relative and absolute addresses is used to indicate [[indirection]].

The only exceptions are where the opcodes of meaningless operations are used for other purposes:

* the opcode for AND register zero with register zero is used for the HALT instruction.
* the opcode for STORE register zero into register zero is used for the [[NOP (code)|NOP]] instruction.

Although the <code>LODZ R0</code> (load register zero with register zero) instruction is supported by the Signetics assembler, its binary encoding is not allowed. The assembler substitutes the binary for the semantically equivalent instruction <code>IORZ R0</code> instead.

===Indexing===
With all arithmetic and logical instructions using absolute (direct) addressing, bits 14 and 13 of the address field are used to indicate the indexing mode as follows:

* 00 no indexing
* 01 indexing with auto increment
* 10 indexing with auto decrement
* 11 indexing only

When indexing is specified, the register defined in the instruction becomes the index register, and the source/destination is implicitly Register zero. For indirect indexing, Post indexing is used, i.e. the indirect address is first fetched from memory and then the index is added to it.

===Branching===
Probably the most mini-computer like aspect of the 2650 is the enormous number (62) of branch (jump) instructions; all these instructions could also use indirection:

* BIRR and BIRA: Increment register and branch if non-zero (R0, R1, R2 or R3) with relative or absolute addressing
* BDRR and BDRA: Decrement register and branch if non-zero (R0, R1, R2 or R3) with relative or absolute addressing
* BRNR and BRNA: branch if register non-zero (R0, R1, R2 or R3) with relative or absolute addressing
* BCTR and BCTA: branch on condition True (zero, greater-than, less-than or unconditional) with relative or absolute addressing
* BCFR and BCFA: branch on condition False (zero, greater-than or less-than) with relative or absolute addressing.
* ZBRR: branch relative to address zero
* BXA: branch indexed

Like the [[Intel 8080]], the 2650 had instructions to conditionally branch to, and return from, a subroutine:

* BSTR and BSTA: branch to subroutine on condition True (zero, greater-than, less-than or unconditional) with relative or absolute addressing
* BSFR and BSFA: branch to subroutine on condition False (zero, greater-than or less-than) with relative or absolute addressing
* BSNR and BSNA: branch to subroutine if register non-zero (R0, R1, R2 or R3) with relative or absolute addressing
* RETC: return from subroutine on condition True (zero, greater-than, less-than or unconditional)
* RETE: return from interrupt on condition True (zero, greater-than, less-than or unconditional)
* ZBSR: branch to subroutine relative to address zero
* BSXA: branch to subroutine indexed

Only the branch instructions using absolute addressing used all 15 bits of the address field as address. Using such a branch instruction was, therefore, the only way to set the two bits in the page register (controlling bits 14 and 13 of the address bus) and changing the current 8 KB page.

==Versions==
* 2650 original version with 1.25 MHz maximum clock frequency
* 2650A improved version (minor fabrication changes to improve stability) 1.25 MHz maximum clock frequency
* 2650A-1 as 2650A with 2 MHz maximum clock frequency
* 2650B
* 2650B-1 as 2650B with 2 MHz maximum clock frequency

The 2650B had the following changes and improvements over the 2650A:<ref>Philips 2650 Series microprocessor short-form manual 02-1979; 9398 209 50011</ref>

* Two new signals{{snd}} "Bus Enable" on pin 15 and "Cycle Last" on pin 25, which marks the instruction fetch cycle.<ref>[https://ztpe.nl/2650/2650b/ 2650B]</ref>
* Program Status Word Upper bits 3 and 4 are settable and testable user flags (unused on the 2650A).
* Two new instructions STPL and LDPL to save and restore the lower status register from memory in order to simplify interrupt processing.
* Single byte register R0 instructions execute faster (one cycle rather than two).

==Second sources==
[[File:Locale_RS6_KL Philips MAB2650.jpg|thumb|right|Philips MAB2650A]]
In 1975, Signetics was sold to [[Philips]] and the 2650 was later incorporated into the [[NXP Semiconductors|Philips Semiconductors]] line. They made a version of the 2650 called the MAB2650A. Valvo, a subsidiary of Philips, sold the 2650 in Germany. Valvo also sold the VA200 single board (Eurocard) 2650 computer with 4 KB PROM/EPROM, 1 KB RAM and four I/O ports.<ref>VALVO VA 200 Mikrocomputer im Europa-Format: VALVO Applikationslaboratorium März 1978</ref>

Other producers of licensed copies of the chip were [[Harris Corporation|Harris]] and [[Intersil]].{{Citation needed|date=September 2025}}

==Peripheral chips==
The 2650 came with a full complement of peripheral chips:

* 2621 Video Encoder (PAL)
* 2622 Video Encoder (NTSC)
* 2636 Programmable Video Interface
* 2637 Universal Video Interface
* 2651 Programmable Communication Interface
* 2652 Multi-Protocol Communications Circuit (incl. Synchronous Data Link Control (SDLC))
* 2653 Polynomial Generator / Checker
* 2655 Programmable Peripheral Interface
* 2656 SMI (System memory interface)
* 2657 Direct Memory Access
* 2661 Enhanced Programmable Communication Interface (EPCI)
* 2670 Display Character and Graphics Generator
* 2671 Programmable Keyboard and Communications Controller
* 2672 Programmable Video Timing Controller
* 2673 Video Attributes Controller

Many of these peripheral chips were designed so they could also be used with other microprocessors, for example the datasheet of the [[SCN2672T|2672]] suggests using it with an [[Intel 8048]] [[microcontroller]].

Philips Technical Note 083 describes how to interface the 2651 PCI to various other microprocessors, such as the 8080, 8085, Z80, 8048 and 6800

Descendants of the 2651/2661 serial communications chips are still sold as the Philips SC26 series.

==2656 System Memory Interface==
The 2656 was specifically designed to augment, and interface with, the 2650 and make a 2-chip computer possible. It contained everything the 2650 lacked to make a complete computer:<ref>2650PC-4000 memory interface emulator using PROM's and FPLA's</ref>

* 2 KB 8-bit mask-programmed ROM program memory
* 128 bytes 8-bit RAM memory
* Clock generator with crystal or RC network
* Power-on reset
* Eight general purpose I/O pins

The I/O pins could be used as an 8-bit I/O port or programmed to generate enable signals for extra RAM, ROM or I/O ports. This was achieved by mask-programming a [[Programmable logic array|Programmable Logic Array]] in the 2656.

To develop and test the design before committing it to production, Philips sold the PC4000, a 2656 emulator board using PROMs and FPLAs to emulate the ROM and PLA in the 2656.

==Notes==
{{notelist}}

==References==
===Citations===
{{Reflist|2}}

===Bibliography===
* {{cite magazine |title=The Signetics 2650 |first=Jamieson |last=Rowe |magazine=Electronics Australia |date=September 1976 |url=http://messui.polygonal-moogle.com/comp/2650.pdf }}

== External links ==
* [https://amigan.1emu.net/releases/#amiarcadia 2650 Emulators]
* [http://datasheets.chipdb.org/Signetics/2650/2650UM.pdf Datasheet]
* [http://www.cpu-world.com/CPUs/2650/ Signetics 2650 family] CPU World
* [https://www.old-computers.com/museum/computer.asp?c=1029&st=1 Instructor 50] Old-computers.com
* [http://www.decodesystems.com/help-wanted/signetics-board.html Adaptable Board Computer] development system complete with 1 KiB PipBug [[Machine code monitor|monitor]] and 512 bytes of [[Random-access memory|RAM]]
* [https://web.archive.org/web/20110717055810/http://www.cpu-museum.com/2650_e.htm the 2650 at www.cpu-museum.com] (archived)
* [http://yesterdaystechnology.com/html/2650.html Electronics Australia 2650 board] at yesterdaystechnology.com
* [http://www.cpushack.com/2016/10/16/signetics-2650-an-ibm-on-a-chip/ Signetics 2650: An IBM on a Chip] retrospective at The CPUSHACK Museum (October 16, 2016)
* [https://www.arcade-museum.com/game_detail.php?game_id=8202 Zaccaria] The Invaders at Museum of the Game
* A 2650 cross assembler is available from https://shop-pdp.net/index.php
{{NXP Semiconductors}}

[[Category:Early microcomputers]]
[[Category:NXP Semiconductors]]
[[Category:8-bit microprocessors]]

File:Locale RS6 Signetics PC1001.jpg

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RS-485: Imported from Wikipedia

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Shift register

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RS-485: Imported from Wikipedia (overwrite)

{{Short description|Computer memory unit using cascaded flip-flops}}
A '''shift register''' is a type of [[digital circuit]] using a cascade of [[flip-flop (electronics)|flip-flops]] where the output of one flip-flop is connected to the input of the next. They share a single [[clock signal]], which causes the data stored in the system to shift from one location to the next. By connecting the last flip-flop back to the first, the data can cycle within the shifters for extended periods, and in this configuration they were used as [[computer memory]], displacing [[delay-line memory]] systems in the late 1960s and early 1970s.

In most cases, several parallel shift registers would be used to build a larger memory pool known as a "[[bit array]]". Data was stored into the array and read back out in parallel, often as a [[computer word]], while each bit was stored serially in the shift registers. There is an inherent trade-off in the design of bit arrays; putting more flip-flops in a row allows a single shifter to store more bits, but requires more clock cycles to push the data through all of the shifters before the data can be read back out again.

Shift registers can have both [[parallel communication|parallel]] and [[serial communication|serial]] inputs and outputs. These are often configured as [[Shift register#Serial-in parallel-out (SIPO)|"serial-in, parallel-out" (SIPO)]] or as [[Shift register#Parallel-in serial-out (PISO)|"parallel-in, serial-out" (PISO)]]. There are also types that have both serial and parallel input and types with serial and parallel output. There are also "bidirectional" shift registers, which allow shifting in both directions: L → R or R → L. The serial input and serial output of a shift register are connected to create a '''circular shift register'''. A PIPO register (parallel in, parallel out) is simply a [[D-type flip-flop|D-type]] [[Register (computer)|register]] and is ''not'' a shift register, but is very fast – an output is given within a single clock pulse. A "universal" shift register provides bidirectional serial-in and serial-out, as well as parallel-in and parallel-out.

== Serial-in serial-out (SISO) ==
=== Destructive readout ===
{| class="wikitable floatright" style="text-align:center"
|+ Sample usage of a 4-bit shift register. Data input is 10110000.
! {{vert header|Time}}
! {{vert header|Output 1}}
! {{vert header|Output 2}}
! {{vert header|Output 3}}
! {{vert header|Output 4}}
|-
! 0
| 0 || 0 || 0 || 0
|-
! 1
| 1 || 0 || 0 || 0
|-
! 2
| 0 || 1 || 0 || 0
|-
! 3
| 1 || 0 || 1 || 0
|-
! 4
| 1 || 1 || 0 || 1
|-
! 5
| 0 || 1 || 1 || 0
|-
! 6
| 0 || 0 || 1 || 1
|-
! 7
| 0 || 0 || 0 || 1
|-
! 8
| 0 || 0 || 0
|0
|}

These are the simplest kind of shift registers. The data string is presented at "data in" and is shifted right one stage each time "data advance" is brought [[Logic level|high]]. At each advance, the bit on the far left (i.e. "data in") is shifted into the first [[flip-flop (electronics)|flip-flop]]'s output. The bit on the far right (i.e. "data out") is shifted out and lost.

The data is stored after each on the "Q" output, so there are four storage "slots" available in this arrangement, hence it is a 4-bit register. To give an idea of the shifting pattern, imagine that the register holds 0000 (so all storage slots are empty). As "data in" presents 1,0,1,1,0,0,0,0 (in that order, with a pulse at "data advance" each time—this is called clocking or strobing) to the register, this is the result. The right hand column corresponds to the right-most flip-flop's output pin, and so on.

So the serial output of the entire value is 00010110. It can be seen that if data were to be continued to input, it would get exactly what was put in (10110000), but offset by four "data advance" cycles. This arrangement is the hardware equivalent of a [[Queue (data structure)|queue]]. Also, at any time, the whole register can be set to zero by bringing the reset (R) pins high.

This arrangement performs ''destructive readout''{{snd}} each datum is lost once it has been shifted out of the right-most bit.

==Serial-in parallel-out (SIPO)==

[[Image:4-Bit SIPO Shift Register.svg|center]]

This configuration allows conversion from serial to parallel format. Data input is serial, as described in the SISO section above. Once the data has been clocked in, it may be either read off at each output simultaneously, or it can be shifted out.

In this configuration, each flip-flop is [[Signal edge|edge triggered]]. All flip-flops operate at the given clock frequency. Each input bit makes its way down to the Nth output after N clock cycles, leading to parallel output.

In cases where the parallel outputs should not change during the serial loading process, it's desirable to use a latched or [[Data buffer|buffered]] output. In a latched shift register (such as the [[List of 7400 series integrated circuits|74595]]) the serial data is first loaded into an internal buffer register, then upon receipt of a load signal the state of the buffer register is copied into a set of output registers. In general, the practical application of the serial-in/parallel-out shift register is to convert data from serial format on a single wire to parallel format on multiple wires.

== Parallel-in serial-out (PISO) ==
This configuration has the data input on lines D1 through D4 in parallel format, D1 being the most significant bit. To write the data to the register, the Write/Shift control line must be held LOW. To shift the data, the W/S control line is brought HIGH and the registers are clocked. The arrangement now acts as a PISO shift register, with D1 as the Data Input. However, as long as the number of clock cycles is not more than the length of the data-string, the Data Output, Q, will be the parallel data read off in order. [[Image:4-Bit PISO Shift Register.png|frame|center|4-Bit PISO Shift Register]] The animation below shows the write/shift sequence, including the internal state of the shift register. [[Image:4-Bit PISO Shift Register Seq.gif|center]]

==Uses==
[[File:Locale_RS6_DOV-1X - Toshiba TC4015BP on printed circuit board-9788.jpg|thumb|[[Toshiba]] TC4015BP dual SIPO shift register|135x135px]]

=== Serial and parallel conversion ===
{{See also|SerDes}}
One of the most common uses of a shift register is to convert between serial and parallel interfaces.

=== Delay ===

Serial-in serial-out shift registers can be used as simple delay circuits.<ref>{{Cite patent|number=US4530107A|title=Shift register delay circuit|gdate=1985-07-16|invent1=Williams|inventor1-first=Marshall|url=https://patents.google.com/patent/US4530107A/en}}</ref>

=== Stack ===

Several bidirectional shift registers can also be connected in parallel for a hardware implementation of a [[stack (data structure)|stack]].

=== More I/O pins ===
Shift registers are commonly attached to [[microcontrollers]] when more [[general-purpose input/output]] pins are required than are available, sometimes over a [[Serial Peripheral Interface#Daisy chain configuration|Serial Peripheral Interface in daisy chain configuration]], which allows any number of binary devices to be accessed using only two to four pins, though more slowly than parallel I/O.

For more outputs, SIPO shift registers are used. The parallel outputs of the shift register and the desired state for all those devices can be sent out of the microcontroller using a single serial connection.

For more inputs, PISO shift registers are used. Each binary input (such as a [[Push-button|button]] or more complicated circuitry) is attached to a parallel input of the shift register, then the data is sent back serially to the microcontroller.

=== Pulse extenders ===
Shift registers can also be used as pulse extenders. Compared to [[monostable multivibrator]]s, the timing does not depend on component values, but it requires an external clock, and the timing accuracy is limited by the granularity of this clock. An example of such a pulse extender is the [[Ronja Twister]], wherein five [[List_of_7400-series_integrated_circuits#74x100_–_74x199|74164 shift registers]] create the core of the timing logic this way ([http://ronja.twibright.com/schematics/twister.png schematic]).

=== Data processing ===
In early computers, shift registers were used to handle data processing: two numbers to be added were stored in two shift registers and clocked out into an [[Arithmetic logic unit|arithmetic and logic unit (ALU)]] with the result being fed back to the input of one of the shift registers (the accumulator), which was one bit longer, since binary addition can only result in an answer that has the same size or is one bit longer.

=== Bitshift operations ===
{{Main articles|Bitshifts}}
Many computer languages include [[bitwise operations]] to "shift right" and "shift left" the data in a register, effectively dividing by two or multiplying by two for each place shifted.

=== Shift register memory ===
Very large [[Shift register#Serial-in serial-out (SISO)|serial-in serial-out]] shift registers (thousands of bits in size) were used in a similar manner to the earlier [[delay-line memory]] in some devices built in the early 1970s. Shift registers don't need many pins or address decoding logic, so was much cheaper than [[random-access memory]] back then.<ref>{{Cite web |last=Shirriff |first=Ken |date=2014 |title=Inside the Intel 1405: die photos of a shift register memory from 1970 |url=http://www.righto.com/2014/12/inside-intel-1405-die-photos-of-shift.html |url-status=live |archive-url=https://web.archive.org/web/20230728203329/https://www.righto.com/2014/12/inside-intel-1405-die-photos-of-shift.html |archive-date=2023-07-28 |access-date=2023-08-06 |website=Ken Shirriff's blog}}</ref> Such ''shift register memory'' was sometimes called ''circulating memory''.

[[Datapoint 3300]], for example, stored its [[Computer terminal|terminal]] display of 25 rows of [[Characters per line|72 columns]] of 6-bit upper-case characters using 54 200-bit shift registers (arranged in 6 tracks of 9 packs), providing storage for 1800 characters. The shift register design meant that scrolling the terminal display could be accomplished by simply pausing the display output to skip one line of characters.<ref>{{cite web|url=http://bitsavers.org/pdf/datapoint/3300/70116_3300termMaint_Dec76.pdf|website=bitsavers.org|title=DataPoint 3300 Maintenance Manual|publisher=Datapoint Corporation|date=December 1976}}</ref> A similar design was used for the [[Apple I]]'s terminal.<ref>{{Cite web |last=Shirriff |first=Ken |title=Inside the Apple-1's shift-register memory |url=http://www.righto.com/2022/04/inside-apple-1s-shift-register-memory.html |url-status=live |archive-url=https://web.archive.org/web/20230606065258/http://www.righto.com/2022/04/inside-apple-1s-shift-register-memory.html |archive-date=2023-06-06 |access-date=2023-08-04 |website=Ken Shirriff's blog}}</ref>

==History==
One of the first known examples of a shift register was in the Mark 2 [[Colossus computer|Colossus]], a code-breaking machine built in 1944. It was a six-stage device built of [[vacuum tube]]s and [[thyratron]]s.<ref>{{Citation | last = Flowers |first= Thomas H. |author-link=Tommy Flowers |url=http://www.ivorcatt.com/47c.htm | title =The Design of Colossus |journal=Annals of the History of Computing |volume=5 |issue=3 |year= 1983|page=246 |doi=10.1109/MAHC.1983.10079|s2cid= 39816473 |url-access=subscription }}</ref> A shift register was also used in the [[IAS machine]], built by [[John von Neumann]] and others at the [[Institute for Advanced Study]] in the late 1940s. Shift registers made their way into integrated circuits in the 1960s as evidenced by early patents from [[Frank Wanlass]]<ref>{{cite web | url=https://patents.google.com/patent/US3406346A/en | title=Shift register system }}</ref> and Kent Smith<ref>{{cite web | url=https://patents.google.com/patent/US3683203 | title=Electronic shift register system }}</ref> working at [[General Instrument]].

==See also==
* [[Delay-line memory]]
* [[Linear-feedback shift register]] (LFSR)
* [[Ring counter]]
* [[SerDes]] (Serializer/Deserializer)
* [[Serial Peripheral Interface Bus]]
* [[Shift register lookup table]] (SRL)
* [[Circular buffer]]

==References==
{{Reflist}}

{{Cryptography stream}}

{{Authority control}}

[[Category:Digital registers]]
[[Category:Computer memory]]

File:Locale RS6 DOV-1X - Toshiba TC4015BP on printed circuit board-9788.jpg

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RS-485: Imported from Wikipedia

Imported from Wikipedia

File:Locale RS6 4-Bit PISO Shift Register Seq.gif

2026-05-03T12:39:49Z

RS-485: Imported from Wikipedia

Imported from Wikipedia

File:Locale RS6 4-Bit PISO Shift Register.png

2026-05-03T12:39:48Z

RS-485: Imported from Wikipedia

Imported from Wikipedia

Serial port

2026-05-03T12:39:44Z

RS-485: Imported from Wikipedia (overwrite)

{{Short description|Communication interface transmitting information sequentially}}
{{Use American English|date=April 2022}}
[[File:Locale_RS6_Serielle schnittstelle.jpg|thumb|A [[gender of connectors and fasteners|male]] [[DE-9]] connector on an [[IBM PC compatible]] computer (with serial port symbol) used for an [[RS-232]] serial port]]
[[File:Locale_RS6_RS-232.jpeg|thumb|A female DE-9 connector on an RS-232 cable.]]

A '''serial port''' is a [[serial communication]] [[Interface (computing)|interface]] through which information transfers in or out sequentially one [[bit]] at a time.<ref>{{cite dictionary |dictionary=Webopedia |url=https://www.webopedia.com/definitions/serial-port/ |title=Serial Port Definition & Meaning |first=Vangie |last=Beal |date=September 1996 |access-date=2021-03-08 }}</ref> This is in contrast to a [[parallel port]], which communicates multiple bits simultaneously in [[Parallel communication|parallel]]. Throughout most of the [[history of personal computers]], data has been transferred through serial ports to devices such as [[modem]]s, [[computer terminal|terminal]]s, various [[peripheral]]s, and directly between computers.

While interfaces such as [[Ethernet]], [[FireWire]], and [[USB]] also send data as a serial [[Stream (computing)|stream]], the term ''serial port'' usually denotes [[Computer hardware|hardware]] compliant with [[RS-232]] or a related standard, such as [[RS-485]] or [[RS-422]].

Modern consumer [[personal computer]]s (PCs) have largely replaced serial ports with higher-speed standards, primarily USB. However, serial ports are still frequently used in applications demanding simple, low-speed interfaces, such as industrial automation systems, scientific instruments, [[point of sale]] systems and some industrial and consumer products.

[[Server (computing)|Server]] computers may use a serial port as a control console for diagnostics, while [[networking hardware]] (such as [[Router (computing)|router]]s and [[Network switch|switch]]es) commonly use serial console ports for configuration, diagnostics, and emergency maintenance access. To interface with these and other devices, [[USB-to-serial adapter]]s can quickly and easily add a serial port to a modern PC.

==Hardware==
{{More citations needed section|date=November 2021}}

Modern devices use an [[integrated circuit]] called a [[UART]] to implement a serial port. This IC converts characters to and from [[asynchronous serial]] form, implementing the timing and framing of data specified by the serial protocol in hardware. The IBM PC implements its serial ports, when present, with one or more UARTs.

Very low-cost systems, such as some early [[home computer]]s, would instead use the [[CPU]] to send the data through an [[input/output|output]] pin, using the [[bit banging]] technique. These early home computers often had proprietary serial ports with pinouts and voltage levels incompatible with RS-232.

Before [[large-scale integration]] (LSI) made UARTs common, serial ports were commonly used in [[mainframe]]s and [[minicomputer]]s, which would have multiple small-scale integrated circuits to implement shift registers, logic gates, counters, and all the other logic needed. As PCs evolved, serial ports were included in the [[Super I/O]] chip and then in the [[chipset]].

{{Gallery
| IBM PC Serial Card.jpg | An [[IBM PC]] serial card with a 25-pin connector (obsolete 8-bit [[Industry Standard Architecture|ISA]] card)
| RS232 PCI-E.jpg | A [[PCI Express]] ×1 card with one serial port
| Four-port serial card with an octopus cable.jpg | A four-port serial (RS-232) PCI Express ×1 [[expansion card]] with an [[octopus cable]] that breaks the card's DC-37 connector into four standard DE-9 connectors
| FTDI USB SERIAL.jpg | A converter from USB to an RS-232 compatible serial port—more than a physical transition, it requires a driver in the host system software and a built-in processor to emulate the functions of the [[IBM XT]] compatible serial port hardware.
|UART to USB adapter.jpg|UART to USB adapter
}}

===DTE and DCE===
The individual signals on a serial port are unidirectional and when connecting two devices, the outputs of one device must be connected to the inputs of the other. Devices are divided into two categories: ''[[data terminal equipment]]'' (DTE) and ''[[data circuit-terminating equipment]]'' (DCE). A line that is an output on a DTE device is an input on a DCE device and vice versa, so a DCE device can be connected to a DTE device with a straight-wired cable, in which each pin on one end goes to the same numbered pin on the other end.

Conventionally, computers and terminals are DTE, while peripherals such as [[modem]]s are DCE. If it is necessary to connect two DTE (or DCE) devices together, a cable with reversed TX and RX lines, known as a [[Crossover cable|cross-over]], roll-over or [[null modem]] cable must be used.

===Gender===
Generally, serial port connectors are [[Gender of connectors and fasteners|gendered]], only allowing connectors to mate with a connector of the opposite gender. With [[D-subminiature]] connectors, the male connectors have protruding pins and female connectors have corresponding round sockets.<ref>{{cite web |url=http://www.cisco.com/c/en/us/support/docs/routers/7200-series-routers/12219-17.html |title=Serial Cable Connection Guide |date=2006-08-01 |publisher=CISCO |access-date=2016-01-31}}</ref> Either type of connector can be mounted on equipment or a panel; or terminate a cable.

Connectors mounted on DTE are likely to be male, and those mounted on DCE are likely to be female (with the cable connectors being the opposite). However, this is far from universal; for instance, most serial printers have a female DB25 connector, but they are DTEs.<ref>{{cite web |url=http://ltxfaq.custhelp.com/app/answers/detail/a_id/1216/~/rs232---dte-and-dce-connectors |title=RS232 - DTE and DCE connectors |date=2006-03-29 |publisher=Lantronix |access-date=2016-01-31 |archive-url=https://web.archive.org/web/20151214054632/http://ltxfaq.custhelp.com/app/answers/detail/a_id/1216/~/rs232---dte-and-dce-connectors |archive-date=2015-12-14 |url-status=dead }}</ref> In this circumstance, the appropriately gendered connectors on the cable or a [[gender changer]] can be used to correct the mismatch.

===Connectors===
The only connector specified in the original RS-232 standard was the 25-pin D-subminiature; however, many other connectors have been used to save money or save on physical space, among other reasons. In particular, since many devices do not use all of the 20 signals that are defined by the standard, connectors with fewer pins are often used. While specific examples follow, countless other connectors have been used for RS-232 connections.

The 9-pin [[D-subminiature|DE-9]] connector has been used by most IBM-compatible PCs since the Serial/Parallel Adapter option for the [[PC-AT]], where the 9-pin connector allowed a serial and parallel port to fit on the same card.<ref>{{Cite web|title=IBM PC AT Serial/Parallel Adapter|url=http://www.minuszerodegrees.net/oa/OA%20-%20IBM%20PC%20AT%20Serial_Parallel%20Adapter.pdf|url-status=dead|archive-url=https://web.archive.org/web/20200224102106/http://minuszerodegrees.net/oa/OA%20-%20IBM%20PC%20AT%20Serial_Parallel%20Adapter.pdf|archive-date=2020-02-24}}</ref> This connector has been standardized for RS-232 as [[TIA-574]].

Some miniaturized electronics, particularly [[graphing calculator]]s<ref>{{Cite web|title=TI-73...92+/V200 TI Link Guide|url=http://merthsoft.com/linkguide/cable.html|access-date=2020-08-14|website=merthsoft.com}}</ref> and hand-held [[Amateur radio|amateur]] and [[two-way radio]] equipment,<ref>{{Cite web|title=Technical Section |url=https://www.miklor.com/COM/UV_Technical.php#progcable|access-date=2020-08-14|website=Miklor.com}}</ref> have serial ports using a [[phone connector (audio)|phone connector]], usually the smaller 2.5 or 3.5 mm connectors and the most basic 3-wire interface—transmit, receive and ground.

[[8P8C]] connectors are also used in many devices. The [[EIA/TIA-561]] standard defines a pinout using this connector, while the [[rollover cable]] (or Yost standard) is commonly used on [[Unix]] computers and network devices, such as equipment from [[Cisco Systems]].<ref>{{Cite web|title=Cabling Guide for Console and AUX Ports|url=https://www.cisco.com/c/en/us/support/docs/routers/7000-series-routers/12223-14.html|access-date=2020-08-14|website=Cisco }}</ref>

Many models of [[Macintosh]] favor the related RS-422 standard, mostly using circular [[mini-DIN connector]]s. The Macintosh included a standard set of two ports for connection to a printer and a modem, but some [[PowerBook]] laptops had only one combined port to save space.<ref>{{Cite web |title=Classic Mac Ports |url=https://whitefiles.org/tec/pgs/h10b.htm |access-date=2020-08-14 |website=WhiteFiles.org }}</ref>

[[10P10C]] connectors can be found on some devices.<ref name="National Instruments 2013">{{cite web |url=http://www.ni.com/pdf/manuals/371253e.pdf |publisher=National Instruments |title=Serial Quick Reference Guide |website=NI.com |date=July 2013 |access-date=2021-06-18 }}</ref>

Another common connector is a {{resx|10|2}} [[pin header]] common on motherboards and add-in cards which is usually converted via a [[ribbon cable]] to the more standard 9-pin DE-9 connector (and frequently mounted on a free slot plate or other part of the housing).<ref>{{Cite book |url=https://www.intel.com/content/dam/support/us/en/documents/motherboards/server/s5000pal/sb/s5000pal_s5000xal_tps_r2_0.pdf |title=Intel Server Board S5000PAL/S5000XAL Technical Product Specification |pages=38 }}</ref>

{{Gallery
| CiscoConsoleCable.jpg | A Cisco rollover cable using the 8P8C Yost standard.
| Mac lc printer modem ports.jpg|Pair of female [[Mini DIN-8]] connectors used for [[RS-422]] serial ports on a [[Macintosh LC]] computer.
| CAN Connecteur.svg|Pin numbering looking into a male [[D-subminiature|DE-9]] connector.
| DE-9 Female.svg|Pin numbering looking into a female DE-9 connector.
}}

===Pinouts===
{{See also|RS-232#Data and control signals}}
{| class="wikitable sortable" style="margin:auto; text-align:center;"
|+Pin assignments of common RS-232 signals<ref>{{cite web |url=http://www.hardwarebook.info/Serial_(PC_9) |title=Serial (PC 9) |author-first=Joakim |author-last=Ögren |access-date=2010-07-07 |archive-url=https://web.archive.org/web/20100811173526/http://www.hardwarebook.info/Serial_%28PC_9%29 |archive-date=2010-08-11 }}</ref>
! colspan="4" |Signal !! colspan="11" |Connector pin
|-
! rowspan="2" |Name !! rowspan="2" |[[ITU-T V.24|V.24]] circuit !! rowspan="2" |{{soft hyphen|Abbrev|iation}} !! rowspan="2" |Origin !! rowspan="2" |{{nowrap|[[DB-25]]}} !! rowspan="2" |{{nowrap|[[DE-9]]}} {{nowrap|([[TIA-574]])}} !! rowspan="2" |[[Modified Modular Jack|MMJ]] !! colspan="5" |[[8P8C]] ("RJ45") !! colspan="3" |[[10P10C]] ("RJ50") {{efn|A 10P10C socket can accept a 8P8C plug. In that case, pins 1-8 on the 8P8C plug connect to pins 2-9 in the 10P10C socket.}}
|-
! [[EIA/TIA-561]] !! Yost (DTE)<ref name="Yost">{{cite web |url=http://yost.com/computers/RJ45-serial/ |title=Yost Serial Device Wiring Standard |access-date=2020-05-10 |archive-url=https://web.archive.org/web/20200617132523/http://yost.com/computers/RJ45-serial/ |archive-date=2020-06-17 |url-status=dead }}</ref> !! Yost (DCE)<ref name="Yost" /> !! Cyclades !! [[Digi International|Digi]] (ALTPIN option) !! [[National Instruments|National {{soft hyphen|Instru|ments}}]]<ref name="National Instruments 2013">{{cite web |url=http://www.ni.com/pdf/manuals/371253e.pdf |publisher=National Instruments |title=Serial Quick Reference Guide |website=NI.com |date=July 2013 |access-date=2021-06-18 }}</ref> !! {{soft hyphen|Cy|clades}} !! Digi
|-
| Transmitted Data || 103 || TxD
| [[Data terminal equipment|DTE]] || 2 || 3 || 2 || 6 || 6 || 3 || 3 || 4 || 8 || 4 || 5
|-
| Received Data || 104 || RxD
| [[Data circuit-terminating equipment|DCE]] || 3 || 2 || 5 || 5 || 3 || 6 || 6 || 5 || 9 || 7 || 6
|-
| Data Terminal Ready || 108/2 || DTR
| DTE || 20 || 4 || 1 || 3 || 7 || 2 || 2 || 8 || 7 || 3 || 9
|-
| Data Carrier Detect || 109 || DCD
| DCE || 8 || 1 || {{n/a}} || 2 || rowspan="2" |2 {{efn|The Yost standard combines DSR and DCD. Only one signal may be connected at the DCE end. When using a crossover cable to connect two DTE devices ([[null modem]]) this signal connects to DTR on the other device.}}
|| 7 || 7 || 1 || 10 || 8 || 10
|-
| Data Set Ready|| 107 || DSR
| DCE || 6 || 6 || 6 || rowspan="2" |1 {{efn|EIA/TIA 561 combines DSR and RI,<ref>{{cite web| url = http://www.hardwarebook.info/RS-232D| title = Hardware Book RS-232D}}</ref><ref>{{cite web| url = http://www.t0rchthe.net/rj45console/index.html| title = RS-232D EIA/TIA-561 RJ45 Pinout}}</ref>. Only one signal may be connected at the DCE end. When connecting two DTE devices ([[null modem]]) RI is not used and this signal should be connected to DTR on the other device in parallel with pin 2 (DCD), or, if that is not possible, left unconnected.}} || {{n/a}} || 8 || {{n/a}} || 5 || 9 || 2
|-
| Ring Indicator || 125 || RI
| DCE || 22 || 9 || {{n/a}} || {{n/a}} || {{n/a}} || {{n/a}} || {{n/a}} || 2 || 10 || 1
|-
| Request To Send {{efn|name=rtr|1=The ''Request To Send'' (RTS, V.24 circuit 105) signal pins are, in fact, nearly always used to carry the ''Ready To Receive'' (RTR, V.24 circuit 133) signal, but even when used for this purpose is still universally referred to as ''RTS'' in documentation.}} || 105 (133) {{efn|name=rtr}} || RTS {{efn|name=rtr}}
| DTE || 4 || 7 || {{n/a}} || 8 || 8 || 1 || 1 || 2 || 4 || 2 || 3
|-
| Clear To Send || 106 || CTS
| DCE || 5 || 8 || {{n/a}} || 7 || 1 || 8 || 5 || 7 || 3 || 6 || 8
|-
| Signal Ground {{efn|''Signal Ground'' (G) is a [[Single-ended signaling|common return]] for the other connections.}}|| 102 || G
| {{n/a}} || 7 || 5 || 3, 4 {{efn|name=gg|''Signal Ground'' (G) appears on two pins in some connectors but carry the same signal; the two pins should be connected in parallel at both ends (if possible) to provide a lower impedance connection.}} || 4 || 4, 5 {{efn|name=gg}} || 4, 5 {{efn|name=gg}}|| 4 || 6 || 6 || 5 || 7
|-
| Protective Ground {{efn|''Protective Ground'' (PG), when available, is intended to be connected by each device to its own frame ground or similar for electrical safety. Connecting Protective Ground to Signal Ground is a common practice but not recommended.}} || 101 || PG
| {{n/a}} || 1 || {{n/a}} || {{n/a}} || {{n/a}} || {{n/a}} || {{n/a}} || {{n/a}} || 3 || {{n/a}} || 1 || 4
|}

{{notelist}}

===Hardware abstraction===
Operating systems usually create symbolic names for the serial ports of a computer, rather than requiring programs to refer to them by hardware address.

[[Unix-like]] operating systems usually label the serial port devices {{mono|/dev/tty*}}. ''TTY'' is a common trademark-free abbreviation for ''[[teletype]]'', a device commonly attached to early computers' serial ports, and {{mono|*}} represents a string identifying the specific port; the syntax of that string depends on the operating system and the device.

On [[Linux]], serial ports intended for general communication have names that start with {{mono|/dev/tty}} followed by a type prefix consisting of capital letters and ending with a sequence number starting with {{mono|0}}. For example, [[8250]]/[[16550 UART]] serial ports are named {{mono|/dev/ttyS*}} ({{mono|/dev/ttyS0}}, {{mono|/dev/ttyS1}}, ...etc); USB adapters appear as {{mono|/dev/ttyUSB*}}, {{mono|/dev/ttyACM*}}, or {{mono|/dev/ttyHS*}}; other types have yet other prefixes. Some virtual serial ports not intended for general communication have names that intentionally do not match this pattern.

The [[DOS]] and [[Windows]] environments refer to serial ports as [[COM (hardware interface)|COM]] ports and are named {{mono|COM}} followed by a sequence number beginning with {{mono|1}}: {{mono|COM1}}, {{mono|COM2}}, ..etc.<ref>{{cite news |title=What Is a Com1 Port? |url=https://www.techwalla.com/articles/what-is-a-com1-port |author=Stephen Byron Cooper |newspaper=Techwalla |access-date=2021-09-30}}</ref>

==Common applications==
This list includes some of the more common devices that are connected to the serial port on a PC. Some of these, such as modems and serial mice, are falling into disuse, while others are readily available. Serial ports are very common on most types of [[microcontroller]], where they can be used to communicate with a PC or other serial devices.

{{Div col|colwidth=30em}}
* Dial-up [[modem]]s
* Configuration and management of [[Computer network|networking]] equipment such as [[Router (computing)|routers]], [[Network switch|switches]], [[Firewall (computing)|firewalls]], [[load balancer]]s
* [[GPS]] receivers (typically [[NMEA 0183]] at {{nowrap|4,800 bit/s}})
* [[Bar code scanner]]s and other [[point of sale]] devices
* [[LED]] and [[LCD]] text displays
* [[Satellite phone]]s, low-speed satellite modems and other satellite-based transceiver devices
* [[Flat-panel display]]s to control screen functions by external computer, other AV components or remotes
* Test and measuring equipment such as digital [[multimeter]]s and weighing systems
* Updating [[firmware]] on various consumer devices
* [[CNC controller]]s
* [[Uninterruptible power supply]] management and status reporting
* Stenography or [[Stenotype]] machines
* Software debuggers that run on a second computer
* Console or debugger interface to [[Microprocessor development board|microprocessor development or evaluation board]]s
* Industrial field buses
* [[Printer (computing)|Printer]]s
* [[Computer terminal]], [[teletype]]
* [[Computer network|Networking]] (Macintosh [[AppleTalk]] using RS-422 at {{nowrap|230.4 kbit/s}})
* Serial mouse
{{Div col end}}

Since the control signals for a serial port can be driven by any [[digital signal]], some applications used the control lines of a serial port to monitor external devices, without exchanging serial data. A common commercial application of this principle was for some models of [[uninterruptible power supply]] which used the control lines to signal loss of power, low battery, and other status information. At least some [[Morse code]] training software used a code key connected to the serial port to simulate actual code use; the status bits of the serial port could be sampled very rapidly and at predictable times, making it possible for the software to decipher Morse code.

Serial computer mice and low-power data converters (e.g. RS-232 to 422 converters) may draw their operating power from the received data or control signals.<ref>{{cite web |last1=Chan |first1=Alvin |title=AN-681 PC Mouse Implementation Using COP800 |url=https://www.ti.com/lit/an/snaa005/snaa005.pdf |publisher=National Semiconductor |access-date=29 July 2023 |date=1990}}</ref><ref>{{cite web |title=AN519 Implementing a Simple Serial Mouse Controller |url=https://ww1.microchip.com/downloads/en/Appnotes/00519c.pdf |publisher=Microchip Technology Inc. |access-date=29 July 2023 |date=1997}}</ref>. This mode is also known as "self powered".

==Settings==
{| class="wikitable floatright" style="width: 33%;"
|+ Common serial port speeds
! style=max-width:5em | [[Bit rate]] {{nowrap|(bit/s)}} !! style=max-width:5em | Time per bit (μs) !! style=max-width:6em | [[Windows]] predefined serial port speed<ref>{{Cite web |title=_SERIAL_COMMPROP (ntddser.h) - Windows drivers {{!}} Microsoft Learn |url=https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ntddser/ns-ntddser-_serial_commprop |work=Windows Hardware Developer |publisher=[[Microsoft]] |date=2022-09-01 |access-date=2025-02-08}}</ref><ref name="winbase.h">{{cite web |title=DCB (winbase.h) - Windows apps {{!}} Microsoft Learn |url=https://learn.microsoft.com/en-us/windows/win32/api/winbase/ns-winbase-dcb |work=Windows App Development |publisher=[[Microsoft]] |date=2021-04-01 |access-date=2025-02-08}}</ref> || Common applications
|-
| 75 || 13333.3 || {{yes}} ||
|-
| 110 || 9090.9 || {{yes}} || [[Bell 101 modem]]
|-
| 134.5 || 7434.9 || {{yes}} || [[IBM 2741]] terminal
|-
| 150 || 6666.6 || {{yes}} ||
|-
| 300 || 3333.3 || {{yes}} || [[Bell 103 modem]] or [[ITU-T V.21|V.21]] modem
|-
| 600 || 1666.7 || {{yes}} ||
|-
| 1,200 || 833.3 || {{yes}} || [[Bell 202]], [[Bell 212A]], or [[ITU-T V.22|V.22]] modem
|-
| 1,800 || 555.6 || {{yes}} ||
|-
| 2,400 || 416.7 || {{yes}} || [[V.22bis]] modem
|-
| 4,800 || 208.3 || {{yes}} || [[V.27ter]] modem
|-
| 7,200 || 138.9 || {{yes}} ||
|-
| 9,600 || 104.2 || {{yes}} || [[ITU-T V.32|V.32]] modem
|-
| 14,400 || 69.4 || {{yes}} || [[V.32bis]] modem
|-
| 19,200 || 52.1 || {{yes}} ||
|-
| 31,250 || 32 || {{no}} || [[MIDI]] port
|-
| 38,400 || 26.0 || {{yes}} ||
|-
| 56,000 || 17.9 || {{yes}} || [[ITU-T V.90|V.90]]/[[V.92]] modem
|-
| 57,600 || 17.4 || {{yes}} || [[V.32bis]] modem with [[V.42bis]] compression
|-
| 76,800 || 13.0 || {{no}} ||
|-
| 115,200 || 8.68 || {{yes}} || [[ITU-T V.34|V.34]] modem with [[V.42bis]] compression, low cost serial [[ITU-T V.90|V.90]]/[[V.92]] modem with [[V.42bis]] or [[ITU-T V.44|V.44]] compression
|-
| 125,000 || 8.00 || {{no}} || ISO 11898-3 [[CAN bus]]
|-
| 128,000 || 7.81 || {{yes}} || [[Basic Rate Interface]] [[ISDN]] [[terminal adapter]]
|-
| 230,400 || 4.34 || {{no}} || [[LocalTalk]], [[Econet]], high end serial [[ITU-T V.90|V.90]]/[[V.92]] modem with [[V.42bis]] or [[ITU-T V.44|V.44]] compression<ref>{{Cite web | url = https://www.multitech.com/documents/publications/data-sheets/86002093.pdf | title = MultiModem ZBA | publisher = Multi-Tech Systems, Inc | date = January 2019 | access-date = September 26, 2019 | archive-url = https://web.archive.org/web/20190303121617/https://www.multitech.com/documents/publications/data-sheets/86002093.pdf | archive-date = March 3, 2019 | url-status = dead }}</ref><ref>{{Cite web | url = https://unicom.usr.com/support/3453c/3453c-ug/control_data_rates.html | title = Courier 56K Business Modem: User Guide: Controlling Data Rates | publisher = [[USRobotics]] | date = 2007 | access-date = September 26, 2019 | archive-url = https://web.archive.org/web/20170804100605/http://unicom.usr.com/support/3453c/3453c-ug/control_data_rates.html | archive-date = August 4, 2017 | url-status = live }}</ref>
|-
| 250,000 || 4.0 || {{no}} || [[DMX512]], stage lighting and effects network
|-
| 256,000 || 3.91 || {{Yes}} ||
|}

Serial standards provide for many different operating speeds as well as adjustments to the protocol to account for different operating conditions. The most well-known options are speed, number of data bits per character, parity, and number of stop bits per character.

In modern serial ports using a UART integrated circuit, all these settings can be software-controlled. Hardware from the 1980s and earlier may require setting switches or jumpers on a circuit board.

The configuration for serial ports designed to be connected to a PC has become a de facto standard, usually stated as 9600/8-N-1.

===Speed===
Serial ports use two-level (binary) signaling, so the data rate in bits per second is equal to the symbol rate in [[baud]]. The total speed includes bits for framing (stop bits, parity, etc.) and so the effective data rate is lower than the bit transmission rate. For example, with 8-N-1 character framing, only 80% of the bits are available for data; for every eight bits of data, two more framing bits are sent.

A standard series of rates is based on multiples of the rates for electromechanical [[teleprinter]]s; some serial ports allow many arbitrary rates to be selected, but the speeds on both sides of the connection must match for data to be received correctly. Bit rates commonly supported include 75, 110, 300, 1200, 2400, 4800, 9600, 19,200, 38,400, 57,600 and {{nowrap|115,200 bit/s}}.<ref name="winbase.h"/> Many of these standard modem bit rates are multiples of either {{nowrap|1.2 kbit/s}} (e.g., 19200, 38400, 76800) or {{nowrap|0.9 kbit/s}} (e.g., 57600, 115200).<ref>{{cite web |url=https://cdn.hackaday.io/files/1614916909230944/SX1272_DS_V4.pdf |title=SX1272/73 - 860 MHz to 1020 MHz Low Power Long Range Transceiver Datasheet |publisher=[[Semtech]] |date=January 2019 }}</ref> [[Crystal oscillator]]s with a frequency of 1.843200 MHz are sold specifically for this purpose. This is 16 times the fastest bit rate, and the serial port circuit can easily divide this down to lower frequencies as required.

The capability to set a bit rate does not imply that a working connection will result. Not all bit rates are possible with all serial ports. Some special-purpose protocols, such as [[MIDI]] for musical instrument control, use serial data rates other than the teleprinter standards. Some serial port implementations can automatically choose a bit rate by observing what a connected device is sending and synchronizing to it.

===Data bits===
The number of data bits in each character can be 5 (for [[Baudot code]]), 6 (rarely used), 7 (for true [[ASCII]]), 8 (for most kinds of data, as this size matches the size of a [[byte]]), or 9 (rarely used). 8 data bits are almost universally used in newer applications. 5 or 7 bits generally only make sense with older equipment, such as teleprinters.

Most serial communications designs send the data bits within each byte [[least significant bit]] first. Also possible, but rarely used, is [[most significant bit]] first; this was used, for example, by the [[IBM 2741]] printing terminal. The order of bits is not usually configurable within the serial port interface but is defined by the host system. To communicate with systems that require a different bit ordering than the local default, local software can re-order the bits within each byte just before sending and just after receiving.

===Parity===
{{Main|Parity bit}}

''Parity'' is a method of detecting errors in transmission. When parity is used with a serial port, an extra data bit is sent with each data character, arranged so that the number of 1 bits in each character, including the parity bit, is always odd or always even. If a byte is received with the wrong number of 1s, then it must have been corrupted. Correct parity does not necessarily indicate absence of corruption as a corrupted transmission with an even number of errors will pass the parity check. A single parity bit does not allow implementation of [[error correction]] on each character, and [[communication protocol]]s working over serial data links will typically have higher-level mechanisms to ensure data validity and request retransmission of data that has been incorrectly received.

The parity bit in each character can be set to one of the following:

* '''None (N)''' means that no parity bit is sent and the transmission is shortened.
* '''Odd (O)''' means that the parity bit is set so that the number of 1 bits is odd.
* '''Even (E)''' means that the parity bit is set so that the number of 1 bits is even.
* '''Mark (M)''' parity means that the parity bit is always set to the mark signal condition (1 bit value).
* '''Space (S)''' parity always sends the parity bit in the space signal condition (0 bit value).

Aside from uncommon applications that use the last bit (usually the 9th) for some form of addressing or special signaling, mark or space parity is uncommon, as it adds no error detection information.

Odd parity is more useful than even parity since it ensures that at least one state transition occurs in each character, which makes it more reliable at detecting errors like those that could be caused by serial port speed mismatches. The most common parity setting, however, is ''none'', with error detection handled by a communication protocol.

To allow detection of messages damaged by [[line noise]], electromechanical teleprinters were arranged to print a special character when received data contained a parity error.

===Stop bits===
Stop bits sent at the end of every character allow the receiving signal hardware to detect the end of a character and to resynchronize with the character stream. Electronic devices usually use one stop bit. If slow electromechanical [[teleprinter]]s are used, one-and-one-half or two stop bits may be required.

===Conventional notation===
[[File:Locale_RS6_Puerto serie Rs232.png|frame|In this diagram, two [[byte]]s are sent, each consisting of a start bit, followed by eight data bits (bits 0-7), and one stop bit, for a 10-bit character frame in 8N1 format. The line on a diagram staying up indicates an excited ("mark" or 1) state of the line, low − unasserted ("space" or 0) state. Both up and low lines drawn for a bit (forming a square) indicate a data bit with value that can be either 0 or 1]]
The data/parity/stop (D/P/S) conventional notation specifies the framing of a serial connection. The most common configuration for the [[Personal computer|personal computing devices]] is '''8-N-1''' (also spelled as 8N1, 8-None-1<ref name="modemhelp"/>), in which there is one start bit, eight ("8") data bits, no ("N") parity bit, and one ("1") stop bit.<ref>{{cite web |title=Definition of N-8-1 |url=https://www.pcmag.com/encyclopedia/term/n-8-1 |website=PCMAG |language=en}}</ref> In this notation, the parity bit is not included into the count of the data bits. For example, 7/E/1 (7E1) means that an even parity bit is added to the 7 data bits for a total of 8 bits between the start and stop bits.

The abbreviation is usually given together with the line speed in [[bits per second]], as in "9600–8-N-1". The speed (or [[baud rate]]) includes bits for [[Data frame|framing]] (stop bits, parity, etc.), thus the effective data rate is lower than the baud rate. For 8-N-1 encoding, only 80% of the bits are available for data (for every eight bits of data, ten bits are sent over the serial link — one start bit, the eight data bits, and the one stop bit).<ref name="modemhelp">{{cite web
| url = http://www.modemhelp.net/faqs/8n1.shtml
| title = What does 8-N-1 mean?
| access-date = 2013-12-25
| publisher = modemhelp.net
}}</ref>

===Flow control===
[[Flow control (data)|Flow control]] is used in circumstances where a transmitter might be able to send data faster than the receiver is able to process it. To cope with this, serial lines often incorporate a [[Handshake (computing)|handshaking]] method. There are ''hardware'' and ''software'' handshaking methods.

'''Hardware handshaking''' is done with extra signals, often the RS-232 RTS/CTS or DTR/DSR signal circuits. RTS and CTS are used to control data flow, signaling, for instance, when a buffer is almost full. Per the RS-232 standard and its successors, DTR and DSR are used to signal that equipment is present and powered up so are usually asserted at all times. However, non-standard implementations exist, for example, printers that use DTR as flow control.

'''Software handshaking''' is done for example with [[ASCII]] control characters [[XON/XOFF]] to control the flow of data. The XON and XOFF characters are sent by the receiver to the sender to control when the sender will send data; that is, these characters go in the opposite direction to the data being sent. The system starts in the ''sending allowed'' state. When the receiver's buffers approach capacity, the receiver sends the XOFF character to tell the sender to stop sending data. Later, after the receiver has emptied its buffers, it sends an XON character to tell the sender to resume transmission. It is an example of [[in-band signaling]], where control information is sent over the same channel as its data.

The advantage of hardware handshaking is that it can be extremely fast, it works independently of imposed meaning, such as ASCII on the transferred data, and it is [[state (computer science)|stateless]]. Its disadvantage is that it requires more hardware and cabling, and both ends of the connection must support the hardware handshaking protocol used.

The advantage of software handshaking is that it can be done with absent or incompatible hardware handshaking circuits and cabling. The disadvantage, common to all in-band control signaling, is that it introduces complexities in ensuring that control messages get through even when data messages are blocked, and data can never be mistaken for control signals. The former is normally dealt with by the operating system or device driver; the latter normally by ensuring that control codes are [[escape sequence|escaped]] (such as in the [[Kermit protocol]]) or omitted by design (such as in [[ANSI escape code|ANSI terminal control]]).

If '''no handshaking''' is employed, an overrun receiver might simply fail to receive data from the transmitter. Approaches for preventing this include reducing the speed of the connection so that the receiver can always keep up, increasing the size of [[data buffer|buffers]] so it can keep up averaged over a longer time, using delays after time-consuming operations (e.g. in [[termcap]]) or employing a mechanism to resend data which has not been received correctly (e.g. [[Transmission Control Protocol|TCP]]).

==See also==
* {{Section link|List of Bluetooth profiles|Serial Port Profile (SPP)}}
* {{Annotated link|Serial cable}}
* {{Annotated link|Serial over LAN}}
* [[Teleprinter]]{{snd}}Device that motivated serial port development
* {{Annotated link|Virtual COM port}}

==References==
{{Reflist}}

==Further reading==
* ''Serial Port Complete: COM Ports, USB Virtual COM Ports, and Ports for Embedded Systems''; 2nd Edition; Jan Axelson; Lakeview Research; 380 pages; 2007; {{ISBN|978-1-931-44806-2}}.

==External links==
{{Wikibooks|Programming:Serial Data Communications}}
* {{Commons category-inline}}
* [https://pinoutguide.com/SerialPorts/ RS-232 and other serial port pinouts list]

{{Basic computer components}}

[[Category:Computer connectors]]
[[Category:Legacy hardware]]
[[Category:Out-of-band management]]
[[Category:Serial buses]]
[[Category:IBM PC compatibles]]

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Serial communications

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#REDIRECT [[Serial communication]]

Serial Line Internet Protocol

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RS-485: Imported from Wikipedia (overwrite)

{{Short description|Internet Protocol encapsulation for serial ports and router connections}}
{{IPstack}}

The '''Serial Line Internet Protocol''' ('''SLIP''')<ref>{{cite news |newspaper=[[The New York Times]]
|url=http://www.nytimes.com/library/cyber/qa/0531freed.html
|title=Internet Q&A |date=May 31, 1996}}</ref><ref>{{cite news |newspaper=[[The New York Times]]
|url=https://www.nytimes.com/1994/05/08/business/the-executive-computer-for-befuddled-newcomers-easier-access-to-the-internet.html
|title=The Executive Computer; For Befuddled Newcomers, Easier Access
|date=May 8, 1994}}</ref> is an [[encapsulation (networking)|encapsulation]] of the [[Internet Protocol]]{{efn|SLIP does not actually care about the internal structures of IP: any [[network layer]] protocols can be sent over the wire.}} designed to work over [[serial port]]s and [[router (computing)|router]] connections. It is documented in {{IETF RFC|1055}}. On personal computers, SLIP has largely been replaced by the [[Point-to-Point Protocol]] (PPP), which is better engineered, has more features, and does not require its IP address configuration to be set before it is established. On [[microcontrollers]], however, SLIP is still the preferred way of encapsulating [[Internet Protocol|IP packets]], due to its very small overhead.

Some people refer to the successful and widely used RFC 1055 Serial Line Internet Protocol as "Rick Adams' SLIP",<ref name="rfc1547">{{IETF RFC|1547}}: "Requirements for an Internet Standard Point-to-Point Protocol" </ref> to avoid confusion with other proposed protocols named "SLIP". Those other protocols include the much more complicated {{IETF RFC|914}} appendix D [[Serial Line Interface Protocol]].<ref name="rfc1547" />

==Description==

{| class="wikitable"
|-
! Hex value !! Dec Value !! Oct Value !! Abbreviation !! Description
|-
| 0xC0 || 192 || 300|| END || Frame End
|-
| 0xDB || 219 || 333 || ESC || Frame Escape
|-
| 0xDC || 220 || 334 || ESC_END || Transposed Frame End
|-
| 0xDD || 221 || 335 || ESC_ESC || Transposed Frame Escape
|}

SLIP modifies a standard [[TCP/IP]] [[datagram]] by:

* appending a special "END" [[byte]] to it, which distinguishes datagram boundaries in the byte stream,
* if the END byte occurs in the data to be sent, the two byte sequence ESC, ESC_END is sent instead,
* if the ESC byte occurs in the data, the two byte sequence ESC, ESC_ESC is sent.
* variants of the protocol may begin, as well as end, packets with END.

SLIP requires a serial port [[computer configuration|configuration]] of 8 [[data]] [[bit]]s, no [[parity bit|parity]], and either [[Electronic Industries Alliance|EIA]] hardware [[flow control (data)|flow control]], or CLOCAL mode (3-wire [[null-modem]]) [[UART]] operation settings.

SLIP does not provide [[error detection]], being reliant on [[upper layer protocol]]s for this. Therefore, SLIP on its own is not satisfactory over a link which is error-prone, such as a poor quality [[dial-up]] connection.

SLIP escape characters were also required on some modem connections to escape [[Hayes command set]], allowing therefore to pass binary data through those modems that would recognize some characters as commands.

==CSLIP==
A version of SLIP with [[Header (computing)|header]] [[data compression|compression]] is called '''Compressed SLIP''' ('''CSLIP''').<ref>{{cite book
|url=https://www.oreilly.com/library/view/understanding-tcpip/9781904811718/ch04s02.html
|title=Understanding TCP/IP (Chapter 4.2 Compressed SLIP)}}</ref> The compression algorithm used in CSLIP is known as [[Van Jacobson TCP/IP Header Compression]].<ref>{{cite web |first=V. |last=Jacobson |title=Compressing TCP/IP Headers for Low-Speed Serial Links |date=February 1990 |url=http://tools.ietf.org/html/rfc1144}} — introduced the [[Van Jacobson TCP/IP Header Compression]] used by CSLIP</ref> CSLIP has no effect on the data payload of a packet and is independent of any compression by the serial line modem used for transmission. It reduces the [[Transmission Control Protocol]] (TCP) header from twenty [[byte]]s to seven bytes. CSLIP has no effect on [[User Datagram Protocol]] (UDP) datagrams.

== History ==
{{See also|History of the Internet}}
RFC 1055, a "non-standard" for SLIP, traces its origins to the 3COM UNET TCP/IP implementation from the 1980s. Rick Adams added SLIP to the popular [[4.2BSD]] in 1984 and it "quickly caught on". By the time of the RFC (1988), it is described as "commonly used on dedicated serial links and sometimes for dialup purposes".<ref name=rfc1055>{{cite web |title=RFC 1055: Nonstandard for transmission of IP datagrams over serial lines: SLIP |url=https://datatracker.ietf.org/doc/html/rfc1055 |website=IETF Datatracker |language=en |date=1 June 1988}}</ref>

The last version of FreeBSD to include "slattach" (a command for connecting to slip) in the manual database is FreeBSD 7.4, released 2011. The manual claims that auto-negotiation exists for CSLIP. The FreeBSD version is inherited from 4.3BSD.<ref>{{cite web |title=slattach(8) |url=https://man.freebsd.org/cgi/man.cgi?query=slip&apropos=0&sektion=8&manpath=FreeBSD+7.4-RELEASE&arch=default&format=html |website=man.freebsd.org}}</ref>

Linux formerly used the same code base for SLIP and [[KISS (TNC)]]. The split occurred before the start of kernel git history (Linux-2.6.12-rc2, 2005).<ref>{{cite web |last1=Torvalds |first1=Linus |title=History for mkiss.c |website=[[GitHub]] |url=https://github.com/torvalds/linux/blob/9a48d604672220545d209e9996c2a1edbb5637f6/drivers/net/hamradio/mkiss.c |access-date=13 May 2023 |date=13 May 2023}}</ref> The SLIP driver offers a special "6-bit" escaped mode to accommodate modems incapable of handling non-ASCII characters.<ref>{{cite web |last1=Torvalds |first1=Linus |title=drivers/net/slip/Kconfig |website=[[GitHub]] |url=https://github.com/torvalds/linux/blob/master/drivers/net/slip/Kconfig |date=13 May 2023}}</ref> The Linux slattach command (written independently) also has the ability to auto-detect CSLIP support.<ref>{{man|8|slattach|Linux}} "Other possible values are slip (normal SLIP), adaptive (adaptive CSLIP/SLIP)...</ref>

==See also==
* [[Parallel Line Internet Protocol]]
* [[Slirp]]
* [[KA9Q]]
* [[Direct cable connection]]
* [[In-band signaling]]
* [[KISS (amateur radio protocol)]]
*[[Consistent Overhead Byte Stuffing]]

==References==
{{notelist}}
{{Reflist}}

{{Authority control}}

[[Category:Internet protocols]]
[[Category:Link protocols]]
[[Category:Logical link control]]

Sampling (signal processing)

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RS-485: Imported from Wikipedia (overwrite)

{{Short description|Measurement of a signal at discrete time intervals}}
[[Image:Signal Sampling.svg|thumb|300px|Signal sampling representation. The continuous signal ''S''(''t'') is represented with a green colored line while the discrete samples are indicated by the blue vertical lines.]]

In [[signal processing]], '''sampling''' is the reduction of a [[continuous-time signal]] to a [[discrete-time signal]]. A common example is the conversion of a [[sound wave]] to a sequence of "samples".
A '''sample''' is a value of the [[signal]] at a point in time and/or space; this definition differs from [[Sampling (statistics)|the term's usage in statistics]], which refers to a set of such values.{{efn-ua|For example, "number of samples" in signal processing is roughly equivalent to "[[sample size]]" in statistics.}}

A '''sampler''' is a subsystem or operation that extracts samples from a [[continuous signal]]. A theoretical '''ideal sampler''' produces samples equivalent to the instantaneous value of the continuous signal at the desired points.

The original signal can be reconstructed from a sequence of samples, up to the [[Nyquist limit]], by passing the sequence of samples through a [[reconstruction filter]].

== Theory ==
{{See also|Nyquist–Shannon sampling theorem}}

Functions of space, time, or any other dimension can be sampled, and similarly in two or more dimensions.

For functions that vary with time, let <math>s(t)</math> be a continuous function (or "signal") to be sampled, and let sampling be performed by measuring the value of the continuous function every <math>T</math> seconds, which is called the '''sampling interval''' or '''sampling period'''.<ref>{{cite book |title=Communications Standard Dictionary |author=Martin H. Weik |publisher=Springer |year=1996 |isbn=0412083914 |url=https://books.google.com/books?id=jxXDQgAACAAJ&q=Communications+Standard+Dictionary}}</ref><ref name=Moir>{{cite book | title = Rudiments of Signal Processing and Systems | author = Tom J. Moir | publisher = Springer International Publishing AG | year = 2022|pages=459 | isbn = 9783030769475 | url = https://public.ebookcentral.proquest.com/choice/publicfullrecord.aspx?p=6809637|doi=10.1007/978-3-030-76947-5 }}</ref> Then the sampled function is given by the sequence:
: <math>s(nT)</math>, for integer values of <math>n</math>.
{{anchor|Sampling rate}}The '''sampling frequency''' or '''sampling rate''', <math>f_s</math>, is the average number of samples obtained in one second, thus <math>f_s=1/T</math>, with the unit ''samples per second'', sometimes referred to as [[hertz]], for example 48 kHz is 48,000 ''samples per second''.

Reconstructing a continuous function from samples is done by interpolation algorithms. The [[Whittaker–Shannon interpolation formula]] is mathematically equivalent to an ideal [[low-pass filter]] whose input is a sequence of [[Dirac delta functions]] that are modulated (multiplied) by the sample values. When the time interval between adjacent samples is a constant <math>(T)</math>, the sequence of delta functions is called a [[Dirac comb]]. Mathematically, the modulated Dirac comb is equivalent to the product of the comb function with <math>s(t)</math>. That mathematical abstraction is sometimes referred to as ''impulse sampling''.<ref>{{cite book |title=Signals and Systems |author=Rao, R. |isbn=9788120338593 |url=https://books.google.com/books?id=4z3BrI717sMC |publisher=Prentice-Hall Of India Pvt. Limited|year=2008 }}</ref>

Most sampled signals are not simply stored and reconstructed. The fidelity of a theoretical reconstruction is a common measure of the effectiveness of sampling. That fidelity is reduced when <math>s(t)</math> contains frequency components whose cycle length (period) is less than 2 sample intervals (see ''[[Aliasing#Sampling sinusoidal functions|Aliasing]]''). The corresponding frequency limit, in ''cycles per second'' ([[hertz]]), is <math>0.5</math> cycle/sample × <math>f_s</math> samples/second = <math>f_s/2</math>, known as the [[Nyquist frequency]] of the sampler. Therefore, <math>s(t)</math> is usually the output of a [[low-pass filter]], functionally known as an ''anti-aliasing filter''. Without an anti-aliasing filter, frequencies higher than the Nyquist frequency will influence the samples in a way that is misinterpreted by the interpolation process.<ref>[[C. E. Shannon]], "Communication in the presence of noise", [[Proc. Institute of Radio Engineers]], vol. 37, no.1, pp. 10–21, Jan. 1949. [http://www.stanford.edu/class/ee104/shannonpaper.pdf Reprint as classic paper in: ''Proc. IEEE'', Vol. 86, No. 2, (Feb 1998)] {{webarchive|url=https://web.archive.org/web/20100208112344/http://www.stanford.edu/class/ee104/shannonpaper.pdf |date=2010-02-08 }}</ref>

== Practical considerations==
In practice, the continuous signal is sampled using an [[analog-to-digital converter]] (ADC), a device with various physical limitations. This results in deviations from the theoretically perfect reconstruction, collectively referred to as [[distortion]].

Various types of distortion can occur, including:
* [[Aliasing]]. Some amount of aliasing is inevitable because only theoretical, infinitely long functions can have no frequency content above the Nyquist frequency. Aliasing can be made [[arbitrarily small]] by using a [[sufficiently large]] order of the anti-aliasing filter.
* [[Analog-to-digital converter#Jitter|Aperture error]] results from the fact that the sample is obtained as a time average within a sampling region, rather than just being equal to the signal value at the sampling instant.<ref>H.O. Johansson and C. Svensson, "Time resolution of NMOS sampling switches", IEEE J. Solid-State Circuits Volume: 33, Issue: 2, pp. 237–245, Feb 1998.</ref> In a [[capacitor]]-based [[sample and hold]] circuit, aperture errors are introduced by multiple mechanisms. For example, the capacitor cannot instantly track the input signal, and the capacitor can not instantly be isolated from the input signal.
* [[Jitter]] or deviation from the precise sample timing intervals.
* [[Noise (physics)|Noise]], including thermal sensor noise, [[analog circuit]] noise, etc..
* [[Slew rate]] limit error, caused by the inability of the ADC input value to change sufficiently rapidly.
* [[Quantization (signal processing)|Quantization]] as a consequence of the finite precision of words that represent the converted values.
* Error due to other [[non-linear]] effects of the mapping of input voltage to converted output value (in addition to the effects of quantization).

Although the use of [[oversampling]] can completely eliminate aperture error and aliasing by shifting them out of the passband, this technique cannot be practically used above a few GHz, and may be prohibitively expensive at much lower frequencies. Furthermore, while oversampling can reduce quantization error and non-linearity, it cannot eliminate these entirely. Consequently, practical ADCs at audio frequencies typically do not exhibit aliasing or aperture error, and are not limited by quantization error. Instead, analog noise dominates. At RF and microwave frequencies, where oversampling is impractical and filters are expensive, aperture error, quantization error and aliasing can be significant limitations.

Jitter, noise, and quantization are often analyzed by modeling them as random errors added to the sample values. Integration and zero-order hold effects can be analyzed as a form of [[low-pass filter]]ing. The non-linearities of either ADC or DAC are analyzed by replacing the ideal [[linear function]] mapping with a proposed [[nonlinear function]].

== Applications ==

=== Audio sampling ===
[[Digital audio]] systems typically employ [[pulse-code modulation]] (PCM) to encode sound as a series of discrete samples of the electrical level of an analog audio signal. Analog signals are captured (encoded) as PCM samples in analog-to-digital conversion (ADC), and reproduced (decoded) using digital-to-analog conversion (DAC). The encoding used for the storage and transmission of digitised sound data within the system may differ.

When it is necessary to capture audio covering the entire 20–20,000 Hz range of [[auditory system|human hearing]]<ref>
{{cite web
| url=https://hypertextbook.com/facts/2003/ChrisDAmbrose.shtml
| title=Frequency range of human hearing
| first1=Christoper
| last1=D'Ambrose
| year=2003
| first2=Rizwan
| last2=Choudhary
| website=The Physics Factbook
| editor-last=Elert
| editor-first=Glenn
| accessdate=2022-01-22
}}</ref> such as when recording music or many types of acoustic events, audio waveforms are typically sampled at 44.1 kHz ([[Compact Disc Digital Audio|CD]]), 48 kHz, 88.2 kHz, or 96 kHz.<ref>{{cite book |url=https://books.google.com/books?id=WzYm1hGnCn4C&pg=PT200 |pages=200, 446 |last=Self |first=Douglas |title=Audio Engineering Explained |publisher=Taylor & Francis US |year=2012 |isbn=978-0240812731}}</ref> The approximately double-rate requirement is a consequence of the [[Nyquist theorem]]. Sampling rates higher than about 50 kHz to 60 kHz cannot supply more usable information for human listeners. Early [[professional audio]] equipment manufacturers chose sampling rates in the region of 40 to 50 kHz for this reason.

There has been an industry trend towards sampling rates well beyond the basic requirements: such as 96 kHz and even 192 kHz<ref>{{cite web |url=http://www.digitalprosound.com/Htm/SoapBox/soap2_Apogee.htm |title=Digital Pro Sound |access-date=8 January 2014 |archive-date=20 October 2008 |archive-url=https://web.archive.org/web/20081020231427/http://www.digitalprosound.com/Htm/SoapBox/soap2_Apogee.htm |url-status=dead }}</ref> Even though [[ultrasonic]] frequencies are inaudible to humans, recording and mixing at higher sampling rates is effective in eliminating the distortion that can be caused by [[Aliasing#Folding|foldback aliasing]]. Conversely, ultrasonic sounds may interact with and modulate the audible part of the frequency spectrum ([[intermodulation distortion]]), ''degrading'' the fidelity.<ref>{{cite journal|last=Colletti|first=Justin|date=February 4, 2013|title=The Science of Sample Rates (When Higher Is Better—And When It Isn't)|url=https://sonicscoop.com/2016/02/19/the-science-of-sample-rates-when-higher-is-better-and-when-it-isnt/?singlepage=1|journal=Trust Me I'm a Scientist|access-date=February 6, 2013|quote=in many cases, we can hear the sound of higher sample rates not because they are more transparent, but because they are less so. They can actually introduce unintended distortion in the audible spectrum}}</ref><ref>{{Cite web|url=https://soundstagehifi.com/index.php/reader-feedback/126-96khz-vs-192khz|title=96 kHz vs. 192 kHz|last=Siau|first=John|date=21 October 2010|website=SoundStage!HI-FI|quote=be very careful about any claims that 192 kHz sounds better than 96 kHz. Our experience points in the opposite direction.}}</ref><ref>{{Cite web|url=https://audient.com/tutorial/why-dont-audient-interfaces-support-192khz/|title=Why don't Audient Interfaces support 192 kHZ?|website=Audient|quote=We are often asked why the iD and EVO interfaces don’t support 192 kHZ, because after all, aren’t higher-spec numbers better? Well, in this case, not always…}}</ref><ref>{{Cite web|url=https://www.headphonesty.com/2025/05/192khz-worse-44-1khz-most-music/|title=192 kHz Is Worse Than 44.1 kHz for Most Music, According to Experts|website=Headphonesty|date=17 May 2025 |quote=So while 192 kHz may look impressive on a spec sheet, it often leads to more system strain, more distortion, and less clarity, all in service of frequencies no human can actually hear.}}</ref>
One advantage of higher sampling rates is that they can relax the low-pass filter design requirements for [[analog-to-digital converter|ADCs]] and [[digital-to-analog converter|DACs]], but with modern oversampling [[Delta-sigma modulation|delta-sigma-converters]], this advantage is less important.

The [[Audio Engineering Society]] recommends 48 kHz sampling rate for most applications, but gives recognition to 44.1 kHz for CD and other consumer uses, 32 kHz for transmission-related applications, and 96 kHz for higher bandwidth or relaxed [[anti-aliasing filter]]ing.<ref name=AES5>{{citation |url=http://www.aes.org/publications/standards/search.cfm?docID=14 |title=AES5-2008: AES recommended practice for professional digital audio – Preferred sampling frequencies for applications employing pulse-code modulation |publisher=Audio Engineering Society |year=2008 |access-date=2010-01-18}}</ref> Both Lavry Engineering and J. Robert Stuart state that the ideal sampling rate would be about 60 kHz, but since this is not a standard frequency, recommend 88.2 or 96 kHz for recording purposes.<ref>{{Cite web|url=http://www.lavryengineering.com/pdfs/lavry-white-paper-the_optimal_sample_rate_for_quality_audio.pdf|title=The Optimal Sample Rate for Quality Audio|last=Lavry|first=Dan|date=May 3, 2012|website=Lavry Engineering Inc.|quote=Although 60 KHz would be closer to the ideal; given the existing standards, 88.2 KHz and 96 KHz are closest to the optimal sample rate.}}</ref><ref>{{Cite web|url=https://www.gearslutz.com/board/showpost.php?p=7883017&postcount=15&s=b05e50b41d1789054724882582d8351b|title=The Optimal Sample Rate for Quality Audio|last=Lavry|first=Dan|website=Gearslutz|language=en|access-date=2018-11-10|quote=I am trying to accommodate all ears, and there are reports of few people that can actually hear slightly above 20KHz. I do think that 48 KHz is pretty good compromise, but 88.2 or 96 KHz yields some additional margin.}}</ref><ref>{{Cite web|url=https://www.gearslutz.com/board/showpost.php?p=1234224&postcount=74|title=To mix at 96k or not?|last=Lavry|first=Dan|website=Gearslutz|language=en|access-date=2018-11-10|quote=Nowdays [sic] there are a number of good designers and ear people that find 60-70KHz sample rate to be the optimal rate for the ear. It is fast enough to include what we can hear, yet slow enough to do it pretty accurately.}}</ref><ref>{{Cite book|title=Coding High Quality Digital Audio|last=Stuart|first=J. Robert|date=1998|quote=both psychoacoustic analysis and experience tell us that the minimum rectangular channel necessary to ensure transparency uses linear PCM with 18.2-bit samples at 58 kHz. ... there are strong arguments for maintaining integer relationships with existing sampling rates – which suggests that 88.2 kHz or 96 kHz should be adopted.|citeseerx = 10.1.1.501.6731}}</ref>
A more complete list of common audio sample rates is:

{| class="wikitable"
|-
! Sampling rate
! Use
|-
|5,512.5 Hz
|Supported in [[Adobe Flash|Flash]].<ref>{{Cite web |date=2013 |title=SWF File Format Specification - Version 19 |url=https://open-flash.github.io/mirrors/swf-spec-19.pdf}}</ref>
|-
| 8,000 Hz
| [[Telephone]] and encrypted [[walkie-talkie]], [[wireless intercom]] and [[wireless microphone]] transmission; adequate for human speech but without [[sibilance]] (''ess'' sounds like ''eff'' ({{IPAslink|s}}, {{IPAslink|f}})).
|-
| 11,025 Hz
| One quarter the sampling rate of audio CDs; used for lower-quality PCM, MPEG audio and for audio analysis of subwoofer bandpasses.{{Citation needed|date=January 2011}}
|-
| 16,000 Hz
| [[Wideband]] frequency extension over standard [[telephone]] [[narrowband]] 8,000 Hz. Used in most modern [[VoIP]] and [[VVoIP]] communication products.<ref>{{Cite web|url=http://www.voipsupply.com/cisco-hd-voice|title = Cisco VoIP Phones, Networking and Accessories - VoIP Supply}}</ref>{{unreliable source?|date=September 2013}}
|-
| 22,050 Hz
| One half the sampling rate of audio CDs; used for lower-quality PCM and MPEG audio and for audio analysis of low-frequency energy. Suitable for digitizing early 20th century audio formats such as [[78s]] and [[AM Radio]].<ref>{{cite web|url=http://www.restoring78s.co.uk/Procedure%20Part%201.htm |title=The restoration procedure – part 1 |publisher=Restoring78s.co.uk |access-date=2011-01-18|archive-url=https://web.archive.org/web/20090914133005/http://www.restoring78s.co.uk/Procedure%20Part%201.htm|archive-date=2009-09-14|quote=For most records a sample rate of 22050 in stereo is adequate. An exception is likely to be recordings made in the second half of the century, which may need a sample rate of 44100.}}</ref>
|-
| 32,000 Hz
| [[miniDV]] digital video [[camcorder]], video tapes with extra channels of audio (e.g. [[DVCAM]] with four channels of audio), [[Digital Audio Tape|DAT]] (LP mode), Germany's [[:de:Digitales Satellitenradio|Digitales Satellitenradio]], [[NICAM]] digital audio, used alongside analogue television sound in some countries. High-quality digital [[wireless microphone]]s.<ref>{{cite web |url=http://www.zaxcom.com/transmitters.htm |title=Zaxcom digital wireless transmitters |publisher=Zaxcom.com |access-date=2011-01-18 |url-status=dead |archive-url=https://web.archive.org/web/20110209050359/http://zaxcom.com/transmitters.htm |archive-date=2011-02-09 }}</ref> Suitable for digitizing [[FM radio]].{{Citation needed|date=September 2011}}
|-
| 37,800 Hz
| [[CD-ROM#CD-ROM XA extension|CD-XA audio]]
|-
| 44,055.9 Hz
| Used by digital audio locked to [[NTSC]] ''color'' video signals (3 samples per line, 245 lines per field, 59.94 fields per second = 29.97 [[frames per second]]).
|-
| [[44,100 Hz]]
| [[Audio CD]], also most commonly used with [[MPEG-1]] audio ([[VCD]], [[SVCD]], [[MP3]]). Originally chosen by [[Sony]] because it could be recorded on modified video equipment running at either 25 frames per second (PAL) or 30 frame/s (using an NTSC ''monochrome'' video recorder) and cover the 20 kHz bandwidth thought necessary to match professional analog recording equipment of the time. A [[PCM adaptor]] would fit digital audio samples into the analog video channel of, for example, [[PAL]] video tapes using 3 samples per line, 588 lines per frame, 25 frames per second.
|-
| 47,250 Hz
| world's first commercial [[PCM]] sound recorder by [[Nippon Columbia]] (Denon)
|-
| [[48,000 Hz]]
| The standard audio sampling rate used by professional digital video equipment such as tape recorders, video servers, vision mixers and so on. This rate was chosen because it could reconstruct frequencies up to 22 kHz and work with 29.97 frames per second NTSC video, as well as {{nowrap|25 frame/s}}, {{nowrap|30 frame/s}} and {{nowrap|24 frame/s}} systems. With {{nowrap|29.97 frame/s}} systems, it is necessary to handle 1601.6 audio samples per frame, delivering an integer number of audio samples only every fifth video frame.<ref name=AES5/> Also used for sound with consumer video formats like DV, [[digital TV]], [[DVD]], films, and many video streaming platforms such as [[YouTube]] and [[Netflix]].<ref>{{Cite web |title=YouTube audio quality |url=https://www.audiomisc.co.uk/YouTube/SpotTheDifference.html |access-date=2026-04-20 |website=www.audiomisc.co.uk}}</ref> The [[lossless audio]] such as [[FLAC]] can select either 44100 Hz, 48000 Hz or higher.<ref>{{Cite web |date=2026-01-09 |title=HiRes FLAC audio |url=https://support.tidal.com/hc/en-us/articles/17412130162961-HiRes-FLAC-audio |access-date=2026-04-20 |website=TIDAL Support |language=en-US}}</ref> The professional [[serial digital interface]] (SDI) and [[High-definition Serial Digital Interface]] (HD-SDI) used to connect broadcast television equipment together use this audio sampling frequency. Most professional audio gear uses 48 kHz sampling, including [[mixing console]]s, and [[digital recording]] devices.
|-
| 50,000 Hz
| First commercial digital audio recorders from the late 70s from [[3M]] and [[Soundstream]].
|-
| 50,400 Hz
| Sampling rate used by the [[X-80|Mitsubishi X-80]] digital audio recorder.
|-
| 64,000 Hz
| Uncommonly used, but supported by some hardware<ref>{{Cite web|url=http://www.rme-audio.de/en/products/hdsp_9632.php|title=RME: Hammerfall DSP 9632|website=www.rme-audio.de|access-date=2018-12-18|quote=Supported sample frequencies: Internally 32, 44.1, 48, 64, 88.2, 96, 176.4, 192 kHz.}}</ref><ref>{{Cite web|url=https://www.pioneer-audiovisual.eu/uk/products/sx-s30dab|title=SX-S30DAB {{!}} Pioneer|website=www.pioneer-audiovisual.eu|access-date=2018-12-18|quote=Supported sampling rates: 44.1 kHz, 48 kHz, 64 kHz, 88.2 kHz, 96 kHz, 176.4 kHz, 192 kHz|archive-date=2018-12-18|archive-url=https://web.archive.org/web/20181218145630/https://www.pioneer-audiovisual.eu/uk/products/sx-s30dab|url-status=dead}}</ref> and software.<ref>{{Cite web|url=https://steinberg.help/wavelab_pro/v9.5/en/wavelab/topics/master_section/master_section_customize_sample_rate_menu_dialog_r.html|title=Customize Sample Rate Menu|last1=Cristina Bachmann|first1=Heiko Bischoff|last2=Schütte|first2=Benjamin|website=Steinberg WaveLab Pro|language=en-US|access-date=2018-12-18|quote=Common Sample Rates: 64 000 Hz}}</ref><ref>{{Cite web|url=https://getsatisfaction.com/m-audio/topics/m-track-2x2m-cubase-pro-9-can-t-change-sample-rate|title=M Track 2x2M Cubase Pro 9 can ́t change Sample Rate|website=M-Audio|language=en-US|access-date=2018-12-18|quote=[Screenshot of Cubase]|archive-date=2018-12-18|archive-url=https://web.archive.org/web/20181218102147/https://getsatisfaction.com/m-audio/topics/m-track-2x2m-cubase-pro-9-can-t-change-sample-rate|url-status=dead}}</ref>
|-
| 88,200 Hz
| Sampling rate used by some professional recording equipment when the destination is CD (multiples of 44,100 Hz). Some pro audio gear uses (or is able to select) 88.2 kHz sampling, including mixers, EQs, compressors, reverb, crossovers, and recording devices.
|-
| 96,000 Hz
| [[DVD-Audio]], some [[LPCM]] DVD tracks, [[BD-ROM]] (Blu-ray Disc) audio tracks, [[HD DVD]] (High-Definition DVD) audio tracks, and [[Hi-Res Audio]]. Some professional recording and production equipment is able to select 96 kHz sampling. This sampling frequency is twice the 48 kHz standard commonly used with audio on professional equipment.
|-
| 176,400 Hz
| Sampling rate used by [[HDCD]] recorders and other professional applications for CD production. Four times the frequency of 44.1 kHz.
|-
| 192,000 Hz
| [[DVD-Audio]], some [[LPCM]] DVD tracks, [[BD-ROM]] (Blu-ray Disc) audio tracks, and [[HD DVD]] (High-Definition DVD) audio tracks, High-Definition audio recording devices, [[Hi-Res Audio]], and audio editing software. This sampling frequency is four times the 48 kHz standard commonly used with audio on professional video equipment.
|-
| 352,800 Hz
| [[Digital eXtreme Definition]], used for recording and editing [[Super Audio CD]]s, as 1-bit [[Direct Stream Digital|Direct Stream Digital (DSD)]] is not suited for editing. 8 times the frequency of 44.1 kHz.
|-
|384,000 Hz
|Maximum sample rate available in common software.{{cn|date=January 2025}}
|-
| 2,822,400 Hz
| [[Super Audio CD|SACD]], 1-bit [[delta-sigma modulation]] process known as [[Direct Stream Digital]], co-developed by [[Sony]] and [[Philips]].
|-
| 5,644,800 Hz
| Double-Rate DSD, 1-bit [[Direct Stream Digital]] at 2× the rate of the SACD. Used in some professional DSD recorders.
|-
| 11,289,600 Hz
| Quad-Rate DSD, 1-bit [[Direct Stream Digital]] at 4× the rate of the SACD. Used in some uncommon professional DSD recorders.
|-
| 22,579,200 Hz
| Octuple-Rate DSD, 1-bit [[Direct Stream Digital]] at 8× the rate of the SACD. Used in rare experimental DSD recorders. Also known as DSD512.
|-
| 45,158,400 Hz
| Sexdecuple-Rate DSD, 1-bit [[Direct Stream Digital]] at 16× the rate of the SACD. Used in rare experimental DSD recorders. Also known as DSD1024.{{efn-ua|Even higher DSD sampling rates exist, but the benefits of those are likely imperceptible, and the size of those files would be humongous.}}
|}

==== Bit depth ====
{{See also|Audio bit depth}}

Audio is typically recorded at 8-, 16-, and 24-bit depth; which yield a theoretical maximum [[signal-to-quantization-noise ratio]] (SQNR) for a pure [[sine wave]] of, approximately; 49.93 [[Decibel|dB]], 98.09 dB, and 122.17 dB.<ref>{{cite web |url=http://www.analog.com/static/imported-files/tutorials/MT-001.pdf |title=MT-001: Taking the Mystery out of the Infamous Formula, "SNR=6.02N + 1.76dB," and Why You Should Care |access-date=2010-01-19 |archive-date=2022-10-09 |archive-url=https://ghostarchive.org/archive/20221009/http://www.analog.com/static/imported-files/tutorials/MT-001.pdf |url-status=dead }}</ref> CD quality audio uses 16-bit samples. [[Thermal noise]] limits the true number of bits that can be used in quantization. Few analog systems have [[Signal-to-noise ratio|signal to noise ratios]] (SNR) exceeding 120 dB. However, [[digital signal processing]] operations can have very high dynamic range, consequently, it is common to perform mixing and mastering operations at 32-bit [[Audio bit depth#Floating point|floating-point precision]] and then convert to 16- or 24-bit for distribution.

==== Speech sampling ====
Speech signals, i.e., signals intended to carry only human [[speech]], can usually be sampled at a much lower rate. For most [[phoneme]]s, almost all of the energy is contained in the 100 Hz – 4 kHz range, allowing a sampling rate of 8 kHz. This is the sampling rate used by nearly all [[telephony]] systems, which use the [[G.711]] sampling and quantization specifications.{{Citation needed|reason=References are needed for frequency range of human voice, and use of G.711|date=May 2018}}

=== Video sampling ===
{{More citations needed section|date=June 2007}}
[[Standard-definition television]] (SDTV) uses either 720 by 480 [[pixels]] (US [[NTSC]] 525-line) or 720 by 576 pixels (UK [[PAL]] 625-line) for the visible picture area.

[[High-definition television]] (HDTV) uses [[720p]] (progressive), [[1080i]] (interlaced), and [[1080p]] (progressive, also known as Full-HD).

In [[digital video]], the temporal sampling rate is defined as the [[frame rate]]{{snd}}or rather the [[field rate]]{{snd}}rather than the notional [[pixel clock]]. The image sampling frequency is the repetition rate of the sensor integration period. Since the integration period may be significantly shorter than the time between repetitions, the sampling frequency can be different from the inverse of the sample time:
* 50 Hz – [[PAL]] video
* 60 / 1.001 Hz ~= 59.94 Hz – [[NTSC]] video

Video [[digital-to-analog converter]]s operate in the megahertz range (from ~3 MHz for low-quality composite video scalers in early game consoles, to 250 MHz or more for the highest-resolution VGA output).

When analog video is converted to [[digital video]], a different sampling process occurs, this time at the pixel frequency, corresponding to a spatial sampling rate along [[scan line]]s. A common pixel sampling rate is:
* 13.5 MHz – [[CCIR 601]], [[D1 video]]

Spatial sampling in the other direction is determined by the spacing of scan lines in the [[raster]]. The sampling rates and resolutions in both spatial directions can be measured in units of lines per picture height.

Spatial [[aliasing]] of high-frequency [[luma (video)|luma]] or [[chrominance|chroma]] video components shows up as a [[moiré pattern]].

=== 3D sampling ===
The process of [[volume rendering]] samples a 3D grid of [[voxel]]s to produce 3D renderings of sliced (tomographic) data. The 3D grid is assumed to represent a continuous region of 3D space. Volume rendering is common in medical imaging, [[X-ray computed tomography]] (CT/CAT), [[magnetic resonance imaging]] (MRI), [[positron emission tomography]] (PET) are some examples. It is also used for [[seismic tomography]] and other applications.

[[File:Bandpass sampling depiction.svg|thumb|right|255px|The top two graphs depict Fourier transforms of two different functions that produce the same results when sampled at a particular rate. The baseband function is sampled faster than its Nyquist rate, and the bandpass function is undersampled, effectively converting it to baseband. The lower graphs indicate how identical spectral results are created by the aliases of the sampling process.]]

== Undersampling ==
{{Main|Undersampling}}

When a [[bandpass]] signal is sampled slower than its [[Nyquist rate]], the samples are indistinguishable from samples of a low-frequency [[aliasing|alias]] of the high-frequency signal. That is often done purposefully in such a way that the lowest-frequency alias satisfies the [[Nyquist rate|Nyquist criterion]], because the bandpass signal is still uniquely represented and recoverable. Such [[undersampling]] is also known as ''bandpass sampling'', ''harmonic sampling'', ''IF sampling'', and ''direct IF to digital conversion.''<ref>
{{cite book
| title = Mixed-signal and DSP design techniques
| author = Walt Kester
| publisher = Newnes
| year = 2003
| isbn = 978-0-7506-7611-3
| page = 20
| url = https://books.google.com/books?id=G8XyNItpy8AC&pg=PA20
| access-date = 8 January 2014
}}</ref>

== Oversampling ==
{{Main|Oversampling}}

Oversampling is used in most modern analog-to-digital converters to reduce the distortion introduced by practical [[digital-to-analog converter]]s, such as a [[zero-order hold]] instead of idealizations like the [[Whittaker–Shannon interpolation formula]].<ref>{{cite book|title=Signals, Sound, and Sensation|author=William Morris Hartmann|publisher=Springer|year=1997|isbn=1563962837|url=https://books.google.com/books?id=3N72rIoTHiEC&pg=PA485}}</ref>

== Complex sampling {{anchor|Complex}} ==
'''Complex sampling''' (or '''I/Q sampling''') is the simultaneous sampling of two different, but related, waveforms, resulting in pairs of samples that are subsequently treated as [[complex numbers]].{{efn-ua|
Sample pairs are also sometimes viewed as points on a [[constellation diagram]].
}} When one waveform, <math>\hat s(t)</math>, is the [[Hilbert transform]] of the other waveform, <math>s(t)</math>, the complex-valued function, <math>s_a(t)\triangleq s(t)+i\cdot\hat s(t)</math>, is called an [[analytic signal]], whose Fourier transform is zero for all negative values of frequency. In that case, the [[Nyquist rate]] for a waveform with no frequencies ≥ ''B'' can be reduced to just ''B'' (complex samples/sec), instead of <math>2B</math> (real samples/sec).{{efn-ua|
When the complex sample-rate is ''B'', a frequency component at 0.6 ''B'', for instance, will have an alias at −0.4 ''B'', which is unambiguous because of the constraint that the pre-sampled signal was analytic. Also see {{slink|Aliasing|Complex sinusoids}}.
}} More apparently, the [[Baseband#Equivalent baseband signal|equivalent baseband waveform]], <math>s_a(t)\cdot e^{-i2\pi\frac{B}{2}t}</math>, also has a Nyquist rate of <math>B</math>, because all of its non-zero frequency content is shifted into the interval <math>[-B/2,B/2]</math>.

Although complex-valued samples can be obtained as described above, they are also created by manipulating samples of a real-valued waveform. For instance, the equivalent baseband waveform can be created without explicitly computing <math>\hat s(t)</math>, by processing the product sequence, <math>\left[s(nT)\cdot e^{-i2\pi\frac{B}{2}Tn}\right]</math>,{{efn-ua|
When ''s''(''t'') is sampled at the Nyquist frequency (1/''T'' {{=}} 2''B''), the product sequence simplifies to <math>\left [s(nT)\cdot (-i)^n\right ].</math>
}} through a digital low-pass filter whose cutoff frequency is <math>B/2</math>.{{efn-ua|
The sequence of complex numbers is convolved with the impulse response of a filter with real-valued coefficients. That is equivalent to separately filtering the sequences of real parts and imaginary parts and reforming complex pairs at the outputs.
}} Computing only every other sample of the output sequence reduces the sample rate commensurate with the reduced Nyquist rate. The result is half as many complex-valued samples as the original number of real samples. No information is lost, and the original <math>s(t)</math> waveform can be recovered, if necessary.

== See also ==
* [[Crystal oscillator frequencies]]
* [[Downsampling]]
* [[Upsampling]]
* [[Sample abundance]]
* [[Multidimensional sampling]]
* [[In-phase and quadrature components]] and [[I/Q data]]
* [[Sample rate conversion]]
* [[Digitizing]]
* [[Sample and hold]]
* [[Beta encoder]]
* [[Kell factor]]
* [[Bit rate]]
* [[Normalized frequency (digital signal processing)|Normalized frequency]]

== Notes ==
{{notelist-ua}}

== References ==
{{Reflist}}

== Further reading==
* Matt Pharr, Wenzel Jakob and Greg Humphreys, ''Physically Based Rendering: From Theory to Implementation, 3rd ed.'', Morgan Kaufmann, November 2016. {{ISBN|978-0128006450}}. The chapter on sampling ([http://www.pbrt.org/chapters/pbrt_chapter7.pdf available online]) is nicely written with diagrams, core theory and code sample.

== External links ==
* [http://www.stsip.org Journal devoted to Sampling Theory]
* [http://whiteboard.ping.se/SDR/IQ I/Q Data for Dummies]{{snd}} a page trying to answer the question ''Why I/Q Data?''
* [http://webdemo.inue.uni-stuttgart.de/webdemos/02_lectures/uebertragungstechnik_1/sampling_theorem/ Sampling of analog signals]{{snd}} an interactive presentation in a web-demo at the Institute of Telecommunications, University of Stuttgart

{{DSP}}
{{Authority control}}

{{DEFAULTSORT:Sampling Rate}}
[[Category:Digital signal processing]]
[[Category:Signal processing]]
[[Category:Digital audio]]
[[Category:Sound measurements]]
[[Category:Audio engineering]]
[[Category:Film and video technology]]

SIM card

2026-05-03T12:38:37Z

RS-485: Imported from Wikipedia (overwrite)

{{Short description|Integrated circuit card for mobile devices}}
{{Redirect|Micro-SIM|the company|MicroSim Corporation}}
[[file:SIM-Karte von Telefónica O2 Europe - Standard und Micro.jpg|thumb|A typical SIM card (mini-SIM with micro-SIM cutout)]]A '''SIM card''' or '''SIM''' ('''subscriber identity module''') is a type of [[integrated circuit]], often in the form of a [[smart card]]. They are intended to securely store an [[international mobile subscriber identity]] (IMSI) number and its related key, which are used to identify and authenticate subscribers on [[mobile telephone]] devices (such as [[mobile phone]]s, [[Tablet computer|tablets]], and [[laptop]]s). SIMs are also able to run apps and to store arbitrary information like [[address book]] contact information,<ref name=":4" /> and may be protected using a [[Personal identification number|PIN code]] to prevent unauthorized use.

These SIM cards are always used on [[GSM]] phones; for [[Code-division multiple access|CDMA]] phones, they are needed only for [[LTE (telecommunication)|LTE]]-capable handsets. SIM cards are also used in various [[satellite phone]]s, smart watches, computers, or cameras.<ref name="ihs" /> The first SIM cards were the size of [[Bank card|credit and bank cards]]; sizes were reduced several times over the years, usually keeping electrical contacts the same, to fit smaller-sized devices.<ref name="sim-evolution">{{cite web |author1=GSMA Intelligence |title=Understanding SIM evolution |url=https://data.gsmaintelligence.com/api-web/v2/research-file-download?id=18809300&file=understanding-sim-evolution-1482139874006.pdf |url-status=live |archive-url=https://web.archive.org/web/20230320082628/https://data.gsmaintelligence.com/api-web/v2/research-file-download?id=18809300&file=understanding-sim-evolution-1482139874006.pdf |archive-date=20 March 2023 |access-date=2023-05-31 |website=GSMA Intelligence |publisher=GSMA}}</ref> SIMs are transferable between different mobile devices by removing the card itself.

Technically, the actual physical card is known as a [[universal integrated circuit card]] (UICC); this [[smart card]] is usually made of [[Polyvinyl chloride|PVC]] with embedded contacts and [[semiconductor]]s, with the SIM as its primary component. In practice the term "SIM card" is still used to refer to the entire unit and not simply the IC. A SIM contains a unique serial number, integrated circuit card identification (ICCID), international mobile subscriber identity (IMSI) number, security authentication and ciphering information, temporary information related to the local network, a list of the services the user has access to, and four passwords: a [[personal identification number]] (PIN) for ordinary use, and a [[personal unblocking key]] (PUK) for PIN unlocking as well as a second pair (called PIN2 and PUK2 respectively) which are used for managing [[Fixed Dialing Number|fixed dialing number]] and some other functionality.<ref>{{cite web |title=Calling Features on Your Samsung Galaxy Phone |url=https://www.samsung.com/us/support/answer/ANS00086742/ |publisher=[[Samsung]] |at=Limit Calling to Specific Numbers |access-date=2022-04-19 }}</ref><ref>{{cite web|url=https://www.nokia.com/phones/en_us/support/nokia-6-2-user-guide/access-codes|title=Access codes|publisher=[[Nokia]]}}</ref> In Europe, the serial SIM number (SSN) is also sometimes accompanied by an [[International Article Number|international article number]] (IAN) or a [[International Article Number|European article number]] (EAN) required when registering online for the subscription of a prepaid card.[[file:Tf sim both sides.png|thumb|A TracFone Wireless SIM card has no distinctive carrier markings and is only marked as a "SIM card".]]As of 2020, [[eSIM]] is superseding physical SIM cards in some domains, including cellular telephony. eSIM uses a software-based SIM embedded into an irremovable eUICC.

== History and procurement ==
The SIM card is a type of [[smart card]],<ref name="ihs">{{cite news |last1=Tait |first1=Don |title=Smart card IC shipments to reach 12.8 billion units in 2021 |url=https://technology.ihs.com/582859/smart-card-ic-shipments-to-reach-128-billion-units-in-2020 |access-date=24 October 2019 |work=IHS Technology |publisher=IHS Markit |date=25 August 2016 |archive-date=24 October 2019 |archive-url=https://web.archive.org/web/20191024214524/https://technology.ihs.com/582859/smart-card-ic-shipments-to-reach-128-billion-units-in-2020 |url-status=live }}</ref> the basis for which is the [[silicon]] [[integrated circuit]] (IC) chip.<ref name="Chen">{{cite book |last1=Chen |first1=Zhiqun |url=https://books.google.com/books?id=qaG0bwxJ-DEC&pg=PA3 |title=Java Card Technology for Smart Cards: Architecture and Programmer's Guide |date=2000 |publisher=[[Addison-Wesley Professional]] |isbn=9780201703290 |pages=3–4}}</ref> The idea of incorporating a silicon IC chip onto a plastic card originates from the late 1960s.<ref name="Chen"/> Smart cards have since used [[List of MOSFET applications|MOS integrated circuit]] chips, along with [[Semiconductor memory|MOS memory]] technologies such as [[flash memory]] and [[EEPROM]] (electrically [[EPROM]]).<ref name=":1">{{cite book |last1=Veendrick |first1=Harry J. M. |url=https://books.google.com/books?id=Lv_EDgAAQBAJ&pg=PA315 |title=Nanometer CMOS ICs: From Basics to ASICs |date=2017 |publisher=Springer |isbn=9783319475974 |pages=315, 481–2}}</ref>

The SIM was initially specified by the [[ETSI]] in the specification TS 11.11. This describes the physical and logical behaviour of the SIM. With the development of the [[Universal Mobile Telecommunications System]] (UMTS), the specification work was partially transferred to [[3GPP]]. 3GPP is now responsible for the further development of applications like SIM (TS 51.011<ref>{{cite web|url=http://www.3gpp.org/dynareport/51011.htm|title=3GPP specification: 51.011|access-date=29 April 2016|archive-date=28 April 2016|archive-url=https://web.archive.org/web/20160428081421/http://www.3gpp.org/DynaReport/51011.htm|url-status=live}}</ref>) and USIM (TS 31.102<ref>{{cite web|url=http://www.3gpp.org/dynareport/31102.htm|title=3GPP specification: 31.102|access-date=29 April 2016|archive-date=14 April 2016|archive-url=https://web.archive.org/web/20160414214907/http://www.3gpp.org/dynareport/31102.htm|url-status=live}}</ref>) and ETSI for the further development of the physical card [[Universal integrated circuit card|UICC]].

The first SIM card was manufactured in 1991 by [[Munich]] smart-card maker [[Giesecke+Devrient]], who sold the first 300 SIM cards to the Finnish [[wireless network operator]] [[Radiolinja]],<ref name=szasif2011>{{cite book|last=Asif|first=Saad Z.|title=Next Generation Mobile Communications Ecosystem|year=2011|publisher=John Wiley & Sons|isbn=978-1119995814|page=306}}</ref><ref name=":2">{{cite web|url=http://www.gi-de.com/usa/en/about_g_d/company/history/history.jsp|title=G&D – History of Giesecke & Devrient|access-date=29 April 2016|archive-date=24 September 2015|archive-url=https://web.archive.org/web/20150924022122/http://www.gi-de.com/usa/en/about_g_d/company/history/history.jsp|url-status=dead}}</ref> who launched the world's first commercial [[2G]] [[GSM]] cell network that year.<ref>{{Cite web |title=World's First GSM Call was made 20 years ago |url=https://www.fonearena.com/blog/40515/worlds-first-gsm-call-was-made-20-years-ago.html |access-date=2024-07-15 |website=www.fonearena.com}}</ref>

Today, SIM cards are considered ubiquitous, allowing over 8 billion devices to connect to cellular networks around the world daily. According to the International Card Manufacturers Association (ICMA), there were 5.4 billion SIM cards manufactured globally in 2016 creating over $6.5 billion in revenue for traditional SIM card vendors.<ref>{{cite web |title=Official Publication of the International Card Manufacturers Association February 2017 Volume 27 No1 |url=http://pageturnpro2.com.s3-website-us-east-1.amazonaws.com/Publications/201703/1354/77336/PDF/131328561544014816_ICMAFebCM12017Final.pdf |access-date=11 May 2025}}</ref> The rise of cellular IoT and 5G networks was predicted by Ericsson to drive the growth of the addressable market for SIM cards to over 20 billion devices by 2020.<ref name=":3">{{cite web|url=https://www.ericsson.com/res/docs/2015/mobility-report/ericsson-mobility-report-nov-2015.pdf|title=Ericsson Mobility Report November 2015|access-date=28 May 2017|archive-date=17 March 2017|archive-url=https://web.archive.org/web/20170317071236/https://www.ericsson.com/res/docs/2015/mobility-report/ericsson-mobility-report-nov-2015.pdf|url-status=live}}</ref> The introduction of [[ESIM|embedded-SIM]] (eSIM) and [[remote SIM provisioning]] (RSP) from the GSMA<ref name=":0">{{cite web|url=http://www.gsma.com/rsp/|title=GSMA Embedded SIM and RSP|access-date=28 May 2017|archive-date=7 June 2017|archive-url=https://web.archive.org/web/20170607042839/https://www.gsma.com/rsp/|url-status=live}}</ref> may disrupt the traditional SIM card ecosystem with the entrance of new players specializing in "digital" SIM card provisioning and other value-added services for mobile network operators.<ref name=":1" />

== Design ==
[[File:Smartcard chip structure and packaging EN.svg|thumb|SIM chip structure and packaging]]
There are three operating voltages for SIM cards: {{nowrap|5 V}}, {{nowrap|3 V}} and {{nowrap|1.8 V}} ([[ISO/IEC 7816]]-3 classes A, B and C, respectively). The operating voltage of the majority of SIM cards launched before 1998 was {{nowrap|5 V}}. SIM cards produced subsequently are compatible with {{nowrap|3 V}} and {{nowrap|5 V}}. Modern cards support {{nowrap|5 V}}, {{nowrap|3 V}} and {{nowrap|1.8 V}}.<ref name=":1" />

[[File:Locale_RS6_Sim Chip.jpg|thumb|{{convert|4|x|4|mm|adj=on}} silicon chip in a SIM card which has been peeled open. Note the thin gold bonding wires, and the regular, rectangular digital memory areas.]]

Modern SIM cards allow applications to load when the SIM is in use by the subscriber. These applications communicate with the handset or a server using [[SIM Application Toolkit]], which was initially specified by [[3GPP]] in TS 11.14. (There is an identical ETSI specification with different numbering.) ETSI and 3GPP maintain the SIM specifications. The main specifications are: ETSI TS 102 223 (the toolkit for smart cards), ETSI TS 102 241 ([[application programming interface|API]]), ETSI TS 102 588 (application invocation), and ETSI TS 131 111 (toolkit for more SIM-likes). SIM toolkit applications were initially written in native code using proprietary APIs. To provide interoperability of the applications, ETSI chose [[Java Card]].<ref>{{cite web |title=ETSI TS 102 241: UICC API for Java Card™ Release 13 |url=https://www.etsi.org/deliver/etsi_ts/102200_102299/102241/13.00.00_60/ts_102241v130000p.pdf |access-date=8 August 2019 |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308204923/https://www.etsi.org/deliver/etsi_ts/102200_102299/102241/13.00.00_60/ts_102241v130000p.pdf |url-status=live }}</ref> A multi-company collaboration called [[GlobalPlatform]] defines some extensions on the cards, with additional APIs and features like more cryptographic security and [[Radio-frequency identification|RFID]] contactless use added.<ref>{{cite web |title=Specifications Archive: Secure Element (Card) |url=https://globalplatform.org/specs-library/?filter-committee=se |website=GlobalPlatform |language=en |access-date=8 August 2019 |archive-date=31 July 2019 |archive-url=https://web.archive.org/web/20190731103515/https://globalplatform.org/specs-library/?filter-committee=se |url-status=live }}</ref>

== Data ==

SIM cards store network-specific information used to authenticate and identify subscribers on the network. The most important of these are the ICCID, IMSI, [[#Authentication key|authentication key (Ki)]], local area identity (LAI) and operator-specific emergency number. The SIM also stores other [[Mobile network operator|carrier]]-specific data such as the SMSC ([[Short Message service center]]) number, service provider name (SPN), service dialing numbers (SDN), advice-of-charge parameters and value-added service (VAS) applications. (Refer to GSM 11.11.<ref>{{cite web|url=http://www.3gpp.org/dynareport/1111.htm|title=3GPP specification: 11.11|access-date=29 April 2016|archive-date=18 August 2016|archive-url=https://web.archive.org/web/20160818100100/http://www.3gpp.org/dynareport/1111.htm|url-status=live}}</ref>)

SIM cards can come in various data capacities, from {{nowrap|8 KB}} to at least {{nowrap|256 KB}}.<ref name=":2" /> All can store a maximum of 250 contacts on the SIM, but while the {{nowrap|32 KB}} has room for 33 [[Mobile country code]] (MCCs) or ''network identifiers'', the {{nowrap|64 KB}} version has room for 80 MNCs.<ref name=":4" /> This is used by network operators to store data on preferred networks, mostly used when the SIM is not in its home network but is [[roaming]]. The network operator that issued the SIM card can use this to have a phone connect to a preferred network that is more economic for the provider instead of having to pay the network operator that the phone discovered first. This does not mean that a phone containing this SIM card can connect to a maximum of only 33 or 80 networks, instead it means that the SIM card issuer can specify only up to that number of preferred networks. If a SIM is outside these preferred networks, it uses the first or best available network.<ref name=":3" />

=== ICCID ===
Each SIM is internationally identified by its '''integrated circuit card identifier''' ('''ICCID'''). Nowadays ICCID numbers are also used to identify eSIM profiles, not only physical SIM cards. ICCIDs are stored in the SIM cards and are also engraved or printed on the SIM card body during a process called personalisation.

The ICCID is defined by the ITU-T recommendation [[E.118]] as the ''primary account number''.<ref>ITU-T, ITU-T Recommendation [[E.118]], The international telecommunication charge card, [http://www.itu.int/rec/T-REC-E.118 Revision history] {{Webarchive|url=https://web.archive.org/web/20121017235304/http://www.itu.int/rec/T-REC-E.118 |date=17 October 2012 }}, [http://www.itu.int/rec/dologin_pub.asp?lang=e&id=T-REC-E.118-200605-I!!PDF-E&type=items Revision "05/2006"]</ref> Its layout is based on [[ISO/IEC 7812]]. According to E.118, the number can be up to 19 digits long, including a single check digit calculated using the [[Luhn algorithm]]. However, the GSM Phase 1<ref>ETSI, ETSI Recommendation GSM 11.11, Specifications of the SIM-ME Interface, [http://www.3gpp.org/ftp/Specs/archive/11_series/11.11/1111-3G0.ZIP Version 3.16.0] {{Webarchive|url=https://web.archive.org/web/20071127095112/http://www.3gpp.org/ftp/Specs/archive/11_series/11.11/1111-3g0.zip |date=27 November 2007 }}</ref> defined the ICCID length as an opaque data field, 10 octets (20 digits) in length, whose structure is specific to a [[mobile network operator]].

The number is composed of three subparts:
*Issuer identification number (IIN)
*Check digit
*Individual account identification
Their format is as follows.

==== Issuer identification number (IIN) ====
* Maximum of seven digits:
** Major industry identifier (MII), 2 fixed digits, '''89''' for telecommunication purposes.
** [[List of country calling codes|Country code]], 2 or 3 digits, as defined by [[ITU-T]] recommendation [[E.164]].
*** [[North American Numbering Plan|NANP]] countries, apart from Canada, use '''01''', i.e. prepending a zero to their common calling code +1
*** [[Canada]] uses '''302'''
*** [[Russia]] uses '''701''', i.e. appending 01 to its calling code +7
*** [[Kazakhstan]] uses '''997''', even though it shares the calling code +7 with Russia
** Issuer identifier, 1–4 digits.
** Often identical to the [[Mobile country code]] (MCC).<ref name=":5" />

==== Individual account identification ====
* Its length is variable, but every number under one IIN has the same length.
** Often identical to the [[Mobile identification number]] (MIN).<ref name="Chen" />

==== Check digit ====
* Single digit calculated from the other digits using the [[Luhn algorithm]].

With the GSM Phase 1 specification using 10 [[Octet (computing)|octets]] into which ICCID is stored as packed BCD{{clarify|date=February 2024}}, the data field has room for 20 digits with hexadecimal digit "F" being used as filler when necessary. In practice, this means that on GSM cards there are 20-digit (19+1) and 19-digit (18+1) ICCIDs in use, depending upon the issuer. However, a single issuer always uses the same size for its ICCIDs.

As required by E.118, the ITU-T updates a list of all current internationally assigned IIN codes in its Operational Bulletins which are published twice a month (the last as of January 2019 was No. 1163 from 1 January 2019).<ref>{{cite web|url=https://www.itu.int/pub/T-SP-OB.1163-2019|title=Operational Bulletin No. 1163 (1.I.2019)|website=www.itu.int|language=en-US|access-date=2019-01-05|archive-date=5 January 2019|archive-url=https://web.archive.org/web/20190105165046/https://www.itu.int/pub/T-SP-OB.1163-2019|url-status=live}}</ref> ITU-T also publishes complete lists: as of August 2023, the list issued on 1 December 2018 was current, having all issuer identifier numbers before 1 December 2018.<ref>{{cite web|url=https://www.itu.int/pub/T-SP-E.118-2018|title=List of issuer identifier numbers for the international telecommunication charge card (in accordance with Recommendation ITU-T E.118 (05/2006))|date=5 January 2015|website=International Telecommunication Union|access-date=4 January 2019|archive-date=5 January 2019|archive-url=https://web.archive.org/web/20190105060539/https://www.itu.int/pub/T-SP-E.118-2018|url-status=live}}</ref>

=== International mobile subscriber identity (IMSI) ===
SIM cards are identified on their individual operator networks by a unique ''[[international mobile subscriber identity]]'' (IMSI). [[Mobile network operator]]s connect mobile phone calls and communicate with their market SIM cards using their IMSIs. The format is:
* The first three digits represent the [[Mobile country code]] (MCC).
* The next two or three digits represent the [[Mobile network code]] (MNC). Three-digit MNC codes are allowed by E.212 but are mainly used in the United States and Canada. One MCC can have both 2 digit and 3 digit MNCs, an example is 350 007.
* The next digits represent the [[Mobile identification number]] (MSIN).
* Normally there are 10 digits, but can be fewer in the case of a 3-digit MNC or if national regulations indicate that the total length of the IMSI should be less than 15 digits.
* Digits are different from country to country.
{{Anchor|Authentication key}}

=== Authentication key (Ki) ===
The Ki is a 128-bit value used in authenticating the SIMs on a [[GSM]] mobile network (for USIM network, the K{{sub|i}} is still needed but other parameters are also needed). Each SIM holds a unique Ki assigned to it by the operator during the personalisation process. The Ki is also stored in a database (termed [[network switching subsystem#Authentication centre (AuC)|authentication center]] or AuC) on the carrier's network.

The SIM card is designed to prevent someone from getting the Ki by using the [[(U)SIM interface|smart-card interface]]. Instead, the SIM card provides a function, ''Run GSM Algorithm'', that the phone uses to pass data to the SIM card to be signed with the Ki. This, by design, makes using the SIM card mandatory unless the Ki can be extracted from the SIM card, or the carrier is willing to reveal the Ki. In practice, the GSM cryptographic algorithm for computing a signed response (SRES_1/SRES_2: see steps 3 and 4, below) from the Ki has certain vulnerabilities<ref name=":4">{{cite news |title= Hackers crack open mobile network |url= https://www.bbc.co.uk/news/technology-13013577 |publisher= bbc.co.uk |access-date= 13 August 2011 |date= 20 April 2011 |archive-date= 12 August 2011 |archive-url= https://web.archive.org/web/20110812103131/http://www.bbc.co.uk/news/technology-13013577 |url-status= live }}</ref> that can allow the extraction of the Ki from a SIM card and the making of a [[Phone cloning|duplicate SIM card]].

Authentication process:

# When the mobile equipment starts up, it obtains the international mobile subscriber identity (IMSI) from the SIM card, and passes this to the mobile operator, requesting access and authentication. The mobile equipment may have to pass a PIN to the SIM card before the SIM card reveals this information.
# The operator network searches its database for the incoming IMSI and its associated Ki.
# The operator network then generates a random number (RAND, which is a [[cryptographic nonce|nonce]]) and signs it with the Ki associated with the IMSI (and stored on the SIM card), computing another number, that is split into the Signed Response 1 (SRES_1, 32 bits) and the encryption key Kc (64 bits).
# The operator network then sends the RAND to the mobile equipment, which passes it to the SIM card. The SIM card signs it with its Ki, producing Signed Response 2 (SRES_2) and Kc, which it gives to the mobile equipment. The mobile equipment passes SRES_2 on to the operator network.
# The operator network then compares its computed SRES_1 with the computed SRES_2 that the mobile equipment returned. If the two numbers match, the SIM is authenticated and the mobile equipment is granted access to the operator's network. Kc is used to encrypt all further communications between the mobile equipment and the operator.

=== Location area identity ===
The SIM stores network state information, which is received from the [[location area identity]] (LAI). Operator networks are divided into location areas, each having a unique LAI number. When the device changes locations, it stores the new LAI to the SIM and sends it back to the operator network with its new location. If the device is power cycled, it takes data off the SIM, and searches for the prior LAI.

=== SMS messages and contacts ===
Most SIM cards store a number of [[SMS]] messages and phone book contacts. It stores the contacts in simple "name and number" pairs. Entries that contain multiple phone numbers and additional phone numbers are usually not stored on the SIM card. When a user tries to copy such entries to a SIM, the handset's software breaks them into multiple entries, discarding information that is not a phone number. The number of contacts and messages stored depends on the SIM; early models stored as few as five messages and 20 contacts, while modern SIM cards can usually store over 250 contacts.<ref name=":6" />

== Formats ==
SIM cards have been made smaller over the years; functionality is independent of format. Full-size SIM was followed by mini-SIM, micro-SIM, and nano-SIM. SIM cards are also made to embed in devices.

[[File:GSM SIM card evolution.svg|thumb|left|upright=3|From left, full-size SIM (1FF), mini-SIM (2FF), micro-SIM (3FF), and nano-SIM (4FF)]]

{| class="wikitable plainrowheaders" style="text-align:right;"
|+ SIM card formats and dimensions
! scope="col"| SIM card format
! scope="col"| Introduced
! scope="col"| Standard reference
! scope="col"| Length
! scope="col"| Width
! scope="col"| Thickness
|-
! scope="row"| Full-size (1FF)
| 1991
| style="text-align:left;"| [[ISO/IEC 7810]]:2003, ID-1
| {{convert|85.6|mm|in|abbr=on}}
| {{convert|53.98|mm|in|abbr=on}}
| {{convert|0.76|mm|in|abbr=on}}
|-
! scope="row"| Mini-SIM (2FF)
| 1996
| style="text-align:left;"| ISO/IEC 7810:2003, ID-000
| {{convert|25|mm|in|abbr=on}}
| {{convert|15|mm|in|abbr=on}}
| {{convert|0.76|mm|in|abbr=on}}
|-
! scope="row"| Micro-SIM (3FF)
| 2003
| style="text-align:left;"| [[ETSI]] TS 102 221 V9.0.0, Mini-UICC
| {{convert|15|mm|in|abbr=on}}
| {{convert|12|mm|in|abbr=on}}
| {{convert|0.76|mm|in|abbr=on}}
|-
! scope="row"| Nano-SIM (4FF)
| early 2012
| style="text-align:left;"| ETSI TS 102 221 V11.0.0
| {{convert|12.3|mm|in|abbr=on}}
| {{convert|8.8|mm|in|abbr=on}}
| {{convert|0.67|mm|in|abbr=on}}
|-
! scope="row"| Embedded-SIM (eSIM)
| 2016
| style="text-align:left;"| ETSI TS 102.671 V9.0.0
[[JEDEC]] Design Guide 4.8, SON-8 GSMA SGP.22 V1.0
|6 mm (0.23622 in)
|5 mm (0.19685 in)
|0
|}
All versions of the non-embedded SIM cards share the same [[ISO/IEC 7816#7816-2|ISO/IEC 7816]] pin arrangement.

=== {{anchor|2FF}}Mini-SIM ===
[[File:Locale_RS6_Disassembled SIM Card Film.JPG|thumb|The memory chip from a micro-SIM card without the plastic backing plate, next to a [[Dime (United States coin)|US dime]], which is approx. 18 mm in diameter]]
[[File:Locale_RS6_SIM-Card X-ray contrast.jpg|thumb|X-ray image of a mini-SIM, showing the chip and connections]]

The ''mini-SIM'' or (2FF, 2nd form factor) card has the same contact arrangement as the full-size SIM card and is normally supplied within a full-size card carrier, attached by a number of linking pieces. This arrangement (defined in [[ISO/IEC 7810]] as [[ID-1/000]]) lets such a card be used in a device that requires a full-size card{{snd}} or in a device that requires a mini-SIM card, after breaking the linking pieces. As the full-size SIM is obsolete, some suppliers refer to the mini-SIM as a "standard SIM" or "regular SIM".

=== {{anchor|3FF}}Micro-SIM ===
The ''micro-SIM'' (or 3FF) card has the same thickness and contact arrangements, but reduced length and width as shown in the table above.<ref>{{cite web|url=https://www.foned.co.uk/mobile-news/what-is-a-microsim-card|title=What is a microsim card?|publisher=Foned.nl|access-date=14 October 2012|url-status=dead|archive-url=https://archive.today/20130222172411/http://simonlypro.nl/what-is-a-microsim-card-en/|archive-date=22 February 2013}}</ref>

The micro-SIM was introduced by the [[ETSI|European Telecommunications Standards Institute]] (ETSI) along with SCP, [[3GPP]] (UTRAN/GERAN), [[3rd Generation Partnership Project 2|3GPP2]] (CDMA2000), [[Association of Radio Industries and Businesses|ARIB]], [[GSMA|GSM Association]] (GSMA SCaG and GSMNA), GlobalPlatform, [[Liberty Alliance]], and the [[Open Mobile Alliance]] (OMA) for the purpose of fitting into devices too small for a mini-SIM card.<ref name=":5">{{cite web|url=http://docbox.etsi.org//Workshop/2006/Salud%20Mexico/Gaby%20Lenhart%20-%20CENETEC_2006_04.ppt|title=The Smart Card Platform|publisher=ETSI Technical Committee Smart Card Platform (TB SCP)|date=1 April 2006|access-date=30 January 2010|author=Gaby Lenhart|quote=SCP is co-operating on both technical and service aspects with a number of other committees both within and outside the telecommunications sector.|archive-date=24 August 2013|archive-url=https://web.archive.org/web/20130824063005/http://docbox.etsi.org//Workshop/2006/Salud%20Mexico/Gaby%20Lenhart%20-%20CENETEC_2006_04.ppt|url-status=live}}</ref><ref>{{cite magazine|url=https://www.pcmag.com/article2/0,2817,2358489,00.asp|title=Inside the iPad Lurks the 'Micro SIM'|magazine=[[PC Magazine]]|date=27 January 2010|access-date=30 January 2010|last1=Segan|first1=Sascha}}</ref>

The form factor was mentioned in the December 1998 3GPP SMG9 [[UMTS]] Working Party, which is the standards-setting body for GSM SIM cards,<ref name=":6">{{cite web|url=http://www.3gpp.org/ftp/TSG_T/WG3_USIM/TSGT3_01/docs/t3-99003.pdf|title=DRAFT Report of the SMG9 UMTS Working Party, meeting #7 hosted by Nokia in Copenhagen, 15–16 December 1998|publisher=[[3GPP]]|date=25 January 1999|access-date=27 January 2010|quote=One manufacturer stated that it may be difficult to meeting ISO mechanical standards for a combined ID-1/micro-SIM card.|archive-date=23 August 2013|archive-url=https://web.archive.org/web/20130823233353/http://www.3gpp.org/ftp/TSG_T/WG3_USIM/TSGT3_01/docs/t3-99003.pdf|url-status=live}}</ref> and the form factor was agreed upon in late 2003.<ref name="SmartCardTrends">{{cite web|url=http://www.smartcardstrends.com/det_atc.php?idu=287 |title=New form factor for smart cards introduced |publisher=SmartCard Trends |date=8 December 2003 |access-date=30 January 2010 |last1=Antipolis |first1=Sophia |quote=The work item for the so-called Third Form Factor, "3FF", was agreed, after intensive discussions, at the SCP meeting held last week in London. |url-status=usurped |archive-url=https://web.archive.org/web/20100426104206/http://www.smartcardstrends.com/det_atc.php?idu=287 |archive-date=26 April 2010 }}</ref>

The micro-SIM was designed for backward compatibility. The major issue for backward compatibility was the contact area of the chip. Retaining the same contact area makes the micro-SIM compatible with the prior, larger SIM readers through the use of plastic cutout surrounds. The SIM was also designed to run at the same speed (5 MHz) as the prior version. The same size and positions of pins resulted in numerous "How-to" tutorials and YouTube videos with detailed instructions how to cut a mini-SIM card to micro-SIM size.

The chairman of EP SCP, Klaus Vedder, said<ref name="SmartCardTrends" />

{{blockquote|ETSI has responded to a market need from ETSI customers, but additionally there is a strong desire not to invalidate, overnight, the existing interface, nor reduce the performance of the cards.}}

=== {{anchor|4FF}}Nano-SIM ===
After a debate in early 2012 between a few designs created by Apple, [[Nokia]] and [[BlackBerry Limited|RIM]], Apple's design for an even smaller SIM card was accepted by the ETSI.<ref>{{Cite web |last=Ziegler |first=Chris |date=2012-03-26 |title=Nano-SIM war: here's what Apple and Nokia want to put in your next phone |url=https://www.theverge.com/2012/3/26/2904153/apple-vs-nokia-4ff-nano-sim |access-date=2024-04-10 |website=The Verge |language=en}}</ref><ref>{{Cite web |title=New SIM card format for slimmer, smaller phones |url=https://www.etsi.org/newsroom/news/398-news-release-1-june-2012 |access-date=2024-04-10 |website=ETSI |language=en-gb}}</ref> The ''nano-SIM'' (or 4FF) card was introduced in June 2012, when mobile service providers in various countries first supplied it for phones that supported the format. The nano-SIM measures {{convert|12.3|x|8.8|x|0.67|mm|abbr=on}} and reduces the previous format to the contact area while maintaining the existing contact arrangements.<ref>{{Cite web |last= |first= |author-link=ETSI |title=TS 102 221 - V11.0.0 - Smart Cards; UICC-Terminal interface; Physical and logical characteristics (Release 11) |url=https://www.etsi.org/deliver/etsi_ts/102200_102299/102221/11.00.00_60/ts_102221v110000p.pdf}}</ref> A small rim of isolating material is left around the contact area to avoid short circuits with the socket. The nano-SIM can be put into adapters for use with devices designed for 2FF or 3FF SIMs, and is made thinner for that purpose,<ref>{{cite web|url=http://docbox.etsi.org/workshop/2012/201201_SECURITYWORKSHOP/3_INTERNATIONAL_STANDARDIZATION/UICC_ETSISCP_Vedder.pdf|title=The UICC – Recent Work of ETSI TC Smart Card Platform|author=Dr. Klaus Vedder|date=18 January 2012|publisher=ETSI|access-date=22 July 2012|page=12|quote=Thinner to allow adapters so that the 4FF can be "clicked" into adapters for use as a Plug-in SIM or 3FF SIM giving a kind of backward usability | archive-url=https://web.archive.org/web/20170830041146/https://docbox.etsi.org/Workshop/2012/201201_SECURITYWORKSHOP/3_INTERNATIONAL_STANDARDIZATION/UICC_ETSISCP_Vedder.pdf|archive-date=30 August 2017}}</ref> and telephone companies give due warning about this.<ref>{{cite web|url=http://www.virginmobile.com/vm/media/images/howdoi/007017_Leaflet_113x127mm_des_v2_LR.pdf|title=An important guide to inserting your SIM into your mobile|author=Virgin Mobile|access-date=21 January 2017 | archive-url = https://web.archive.org/web/20180125015505/http://www.virginmobile.com/vm/media/images/howdoi/007017_Leaflet_113x127mm_des_v2_LR.pdf | archive-date = 25 January 2018 | quote = You may also have to use one of the enclosed adaptors. If you don't follow these guidelines your phone warranty could be invalidated. We're afraid we can't accept responsibility for any damage to your phone if you choose to ignore this advice.}}</ref> 4FF is {{convert|0.67|mm|in|abbr=on}} thick, compared to the {{convert|0.76|mm|in|abbr=on}} of its predecessors.

== Security ==
In July 2013, Karsten Nohl, a security researcher from SRLabs, described<ref>[http://securitywatch.pcmag.com/mobile-security/313914-encryption-bug-in-sim-card-can-be-used-to-hack-millions-of-phones Encryption Bug in SIM Card Can be Used to Hack Millions of Phones] {{Webarchive|url=https://web.archive.org/web/20130724055849/http://securitywatch.pcmag.com/mobile-security/313914-encryption-bug-in-sim-card-can-be-used-to-hack-millions-of-phones |date=24 July 2013 }}, published 2013-07-21, accessed 2013-07-22</ref><ref name=SRLabs>[https://archive.today/20130721231840/https://srlabs.de/rooting-sim-cards/ Rooting SIM cards], SR Labs, accessed 2013-07-22</ref> vulnerabilities in some SIM cards that supported [[Data Encryption Standard|DES]], which, despite its age, is still used by some operators.<ref name=SRLabs /> The attack could lead to the phone being remotely [[Phone cloning|cloned]] or let someone steal payment credentials from the SIM.<ref name=SRLabs /> Further details of the research were provided at [[Black Hat Briefings|BlackHat]] on 31 July 2013.<ref name=SRLabs /><ref>{{cite web|url=https://www.blackhat.com/us-13/briefings.html#Nohl|title=Black Hat USA 2013|access-date=29 April 2016|archive-date=2 January 2018|archive-url=https://web.archive.org/web/20180102130632/http://www.blackhat.com/us-13/briefings.html#Nohl|url-status=live}}</ref> In response, the [[International Telecommunication Union]] said that the development was "hugely significant" and that it would be contacting its members.<ref>[https://www.reuters.com/article/mobile-hacking-idUSL6N0FR0JD20130721 UPDATE 1-UN warns on mobile cybersecurity bugs in bid to prevent attacks] {{Webarchive|url=https://web.archive.org/web/20220319084019/https://www.reuters.com/article/mobile-hacking-idUSL6N0FR0JD20130721 |date=19 March 2022 }}, Reuters, 2013-07-21, accessed 2013-07-21</ref>

In February 2015, [[The Intercept]] reported that the [[National Security Agency|NSA]] and [[GCHQ]] had stolen the encryption keys (Ki's) used by [[Gemalto]] (now known as [[Thales DIS AIS|Thales DIS]], manufacturer of 2 billion SIM cards annually) <ref>{{Cite web |date=2019-04-02 |title=Thales Completes Acquisition Of Gemalto To Become A Global Leader In Digital Identity And Security {{!}} Thales Group |url=https://www.thalesgroup.com/en/group/journalist/press-release/thales-completes-acquisition-gemalto-become-global-leader-digital |access-date=2023-12-24 |website=www.thalesgroup.com |language=en}}</ref>), enabling these intelligence agencies to monitor voice and data communications without the knowledge or approval of cellular network providers or judicial oversight.<ref>{{cite web|url = https://firstlook.org/theintercept/2015/02/19/great-sim-heist/|title = The Great SIM Heist – How Spies Stole the Keys to the Encryption Castle|date = 19 February 2015|access-date = 19 February 2015|website = The Intercept|publisher = The Intercept (First Look Media)|archive-date = 19 February 2015|archive-url = https://web.archive.org/web/20150219200149/https://firstlook.org/theintercept/2015/02/19/great-sim-heist/|url-status = live}}</ref> Having finished its investigation, Gemalto claimed that it has “reasonable grounds” to believe that the NSA and GCHQ carried out an operation to hack its network in 2010 and 2011, but says the number of possibly stolen keys would not have been massive.<ref>{{cite web|url = https://techcrunch.com/2015/02/25/gemalto-2/|title = Gemalto: NSA/GCHQ Hack 'Probably Happened' But Didn't Include Mass SIM Key Theft|date = 25 February 2015|access-date = 2 April 2015|website = techcrunch.com|archive-date = 30 March 2015|archive-url = https://web.archive.org/web/20150330070411/http://techcrunch.com/2015/02/25/gemalto-2/|url-status = live}}</ref>

In September 2019, Cathal Mc Daid, a security researcher from Adaptive Mobile Security, described<ref>{{Cite web|last=Cimpanu|first=Catalin|title=Simjacker attack exploited in the wild to track users for at least two years|url=https://www.zdnet.com/article/new-simjacker-attack-exploited-in-the-wild-to-track-users-for-at-least-two-years/|access-date=2021-07-28|website=ZDNet|language=en|archive-date=28 July 2021|archive-url=https://web.archive.org/web/20210728160009/https://www.zdnet.com/article/new-simjacker-attack-exploited-in-the-wild-to-track-users-for-at-least-two-years/|url-status=live}}</ref><ref>{{Cite web|title=Simjacker – Next Generation Spying Over Mobile {{!}} Mobile Security News {{!}} AdaptiveMobile|url=https://blog.adaptivemobile.com/simjacker-next-generation-spying-over-mobile|access-date=2021-07-28|website=blog.adaptivemobile.com|date=11 September 2019 |language=en|archive-date=28 July 2021|archive-url=https://web.archive.org/web/20210728154207/https://blog.adaptivemobile.com/simjacker-next-generation-spying-over-mobile|url-status=live}}</ref> how vulnerabilities in some SIM cards that contained the S@T Browser library were being actively exploited. This vulnerability was named [[Simjacker]]. Attackers were using the vulnerability to track the location of thousands of mobile phone users in several countries.<ref>{{Cite news|last=Olson|first=Parmy|date=2019-09-13|title=Hackers Use Spyware to Track SIM Cards|language=en-US|work=[[The Wall Street Journal]]|url=https://www.wsj.com/articles/hackers-use-spyware-to-track-sim-cards-11568400758|access-date=2021-07-28|issn=0099-9660|archive-date=28 July 2021|archive-url=https://web.archive.org/web/20210728154206/https://www.wsj.com/articles/hackers-use-spyware-to-track-sim-cards-11568400758|url-status=live}}</ref> Further details of the research were provided at [[Virus Bulletin|VirusBulletin]] on 3 October 2019.<ref>{{Cite web|title=Virus Bulletin :: Simjacker — the next frontier in mobile espionage|url=https://www.virusbulletin.com/conference/vb2019/abstracts/simjacker-next-frontier-mobile-espionage|access-date=2021-07-28|website=www.virusbulletin.com|archive-date=28 July 2021|archive-url=https://web.archive.org/web/20210728154208/https://www.virusbulletin.com/conference/vb2019/abstracts/simjacker-next-frontier-mobile-espionage|url-status=live}}</ref><ref>{{Cite web|title=Simjacker — Frequently Asked Questions and Demos {{!}} Mobile Security News {{!}} AdaptiveMobile|url=https://blog.adaptivemobile.com/simjacker-frequently-asked-questions|access-date=2021-07-28|website=blog.adaptivemobile.com|date=11 September 2019 |language=en|archive-date=28 July 2021|archive-url=https://web.archive.org/web/20210728154207/https://blog.adaptivemobile.com/simjacker-frequently-asked-questions|url-status=live}}</ref>

== Developments ==
When GSM was already in use, the specifications were further developed and enhanced with functionality such as [[SMS]] and [[General Packet Radio Service|GPRS]]. These development steps are referred as releases by ETSI. Within these development cycles, the SIM specification was enhanced as well: new voltage classes, formats and files were introduced.

=== USIM === 
In GSM-only times, the SIM consisted of the hardware and the software. With the advent of UMTS, this naming was split: the SIM was now an application and hence only software. The hardware part was called UICC. This split was necessary because UMTS introduced a new application, the universal subscriber identity module (USIM). The USIM brought, among other things, security improvements like mutual authentication and longer encryption keys, and an improved address book.

=== UICC ===
{{Main|Universal integrated circuit card}}

"SIM cards" in developed countries today are usually [[universal integrated circuit card|UICCs]] containing at least a SIM application and a USIM application. This configuration is necessary because older GSM only handsets are solely compatible with the SIM application and some UMTS security enhancements rely on the USIM application.

=== Other variants ===
On [[cdmaOne]] networks, the equivalent of the SIM card is the [[Removable User Identity Module|R-UIM]] and the equivalent of the SIM application is the [[CDMA subscriber identity module|CSIM]].

{{anchor|Virtual SIM}}
A ''virtual SIM'' is a mobile phone number provided by a [[mobile network operator]] that does not require a SIM card to connect phone calls to a user's mobile phone.

=== {{anchor|MFF|eSIM}}Embedded SIM (eSIM) ===
{{Main|eSIM}}

[[File:Locale_RS6_Embedded SIM from M2M supplier Eseye with an adapter board for evaluation in a Mini-SIM socket blurred.jpg|thumb|Embedded SIM from M2M supplier Eseye with an adapter board for evaluation in a mini-SIM socket]]

An embedded SIM (eSIM) is a form of programmable SIM that is embedded directly into a device.<ref>{{Cite book |last=Krüssel |first=Peter |url=https://books.google.com/books?id=Ry9mDwAAQBAJ&dq=An+embedded+SIM+(eSIM)+is+a+form+of+programmable+SIM+that+is+embedded+directly+into+a+device.&pg=PA13 |title=Future Telco: Successful Positioning of Network Operators in the Digital Age |date=2018-07-23 |publisher=Springer |isbn=978-3-319-77724-5 |pages=13 |language=en}}</ref> The surface mount format provides the same electrical interface as the full size, 2FF and 3FF SIM cards, but is soldered to a circuit board as part of the manufacturing process. In M2M applications where there is no requirement<ref name=":0" /> to change the SIM card, this avoids the requirement for a connector, improving reliability and security.<ref>{{Cite web |title=IoT SIM Cards: An Introduction |url=https://iot.telenor.com/technologies/introduction-to-iot-sim-cards/ |access-date=2025-11-17 |website=Telenor IoT |language=en-US}}</ref> An eSIM can be [[Remote SIM provisioning|provisioned remotely]]; end-users can add or remove operators without the need to physically swap a SIM from the device or use multiple eSIM profiles at the same time.<ref>{{cite web|url=https://podm2m.com/euicc-future-sim-technology/|title=eUICC – The Future for SIM Technology|date=2019-07-05|website=PodM2M|access-date=18 September 2018|archive-date=29 August 2019|archive-url=https://web.archive.org/web/20190829155231/https://podm2m.com/euicc-future-sim-technology/|url-status=usurped}}</ref><ref>{{Cite web |title=How does an eSIM work? |url=https://support.saily.com/hc/en-us/articles/12823321335580-How-does-an-eSIM-work |access-date=2024-12-23 |website=Saily Help Center |language=en-US}}</ref>

The eSIM standard, initially introduced in 2016, has progressively supplanted traditional physical SIM cards across various sectors, notably in cellular telephony.<ref>{{Cite web |title=The eSIM opportunity |url=https://asianwirelesscomms.com/feature-details?itemid=6680#:~:text=The%20first%20standard%20for%20eSIMs,typically%20been%20developed%20world%20regions. |access-date=2024-08-04 |website=asianwirelesscomms.com |language=en-US}}</ref><ref>{{Cite book |last=Bair |first=John |url=https://books.google.com/books?id=bE8ADQAAQBAJ&dq=The+eSIM+standard+was+first+released+in+2016&pg=PA73 |title=Seeking the Truth from Mobile Evidence: Basic Fundamentals, Intermediate and Advanced Overview of Current Mobile Forensic Investigations |date=2017-11-17 |publisher=Academic Press |isbn=978-0-12-811057-7 |pages=73 |language=en}}</ref>

=== {{anchor|iSIM|nuSIM}}Integrated SIM (iSIM) ===
An integrated SIM (iSIM) is a form of SIM directly integrated into the modem chip or main processor of the device itself. As a consequence they are smaller, cheaper and more reliable than eSIMs, they can improve security and ease the logistics and production of small devices i.e. for [[Internet of things|IoT]] applications. In 2021, [[Deutsche Telekom]] introduced the nuSIM, an "Integrated SIM for IoT".<ref>{{cite web |title=eSIM und nuSIM – was sind die Unterschiede? Telekom arbeitet an nuSIM |language=de |publisher=Portalavenue GmbH |work=M2M-Kommunikation.de |url=https://www.m2m-kommunikation.de/beratung/esim-und-nusim-was-sind-die-unterschiede.html |access-date=2022-06-22 |url-status=live |archive-url=https://web.archive.org/web/20220622171155/https://www.m2m-kommunikation.de/beratung/esim-und-nusim-was-sind-die-unterschiede.html |archive-date=2022-06-22}}</ref><ref>{{cite web |title=nuSIM: Unsere innovative iSIM-Lösung |language=de |publisher=[[Deutsche Telekom]] |url=https://iot.telekom.com/de/netze-tarife/iot-sim-karten/nusim |access-date=2022-06-22 |url-status=live |archive-url=https://web.archive.org/web/20220622171401/https://iot.telekom.com/de/netze-tarife/iot-sim-karten/nusim |archive-date=2022-06-22}}</ref><ref>{{cite web |title=nuSIM – die integrierte SIM für das Internet der Dinge |language=de |publisher=[[Deutsche Telekom]] |date=2022-02-15 |orig-date=2021 |author-first=Daniel |author-last=Kunz |url=https://iot.telekom.com/de/blog/nusim-die-integrierte-sim-fuer-das-internet-der-dinge |access-date=2022-06-22 |archive-url=https://web.archive.org/web/20211123030915/https://iot.telekom.com/de/blog/nusim-die-integrierte-sim-fuer-das-internet-der-dinge |archive-date=2021-11-23}}</ref>

== Usage in mobile phone standards ==
[[File:Locale_RS6_SIM Karten (47514651302).jpg|thumb|SIM cards of various German mobile operators]]
The use of SIM cards is mandatory in [[GSM]] devices.<ref>{{Cite web |last=Bolton |first=David |date=2013-08-26 |title=New Vulnerabilities in Older SIM Cards |url=https://www.dice.com/career-advice/older-sim-cards-have-vulnerabilities-001 |access-date=2024-08-04 |website=Dice Insights |language=en}}</ref><ref>{{Cite book |last1=Correia |first1=Luis M. |url=https://books.google.com/books?id=DbucHQnOMW8C&dq=The+use+of+SIM+cards+is+mandatory+in+%22GSM+devices%22.&pg=PA300 |title=Architecture and Design for the Future Internet: 4WARD Project |last2=Abramowicz |first2=Henrik |last3=Johnsson |first3=Martin |last4=Wünstel |first4=Klaus |date=2011-01-06 |publisher=Springer Science & Business Media |isbn=978-90-481-9346-2 |pages=300 |language=en}}</ref>

The [[satellite phone]] networks [[Iridium Communications|Iridium]], [[Thuraya]] and [[Inmarsat]]'s [[Broadband Global Area Network|BGAN]] also use SIM cards. Sometimes, these SIM cards work in regular GSM phones and also allow GSM customers to roam in satellite networks by using their own SIM cards in a satellite phone.

Japan's 2G [[Personal Digital Cellular|PDC]] system (which was shut down in 2012; [[SoftBank Group|SoftBank Mobile]] shut down PDC from 31 March 2010) also specified a SIM, but this has never been implemented commercially. The specification of the interface between the Mobile Equipment and the SIM is given in the [[Association of Radio Industries and Businesses|RCR]] STD-27 annexe 4. The Subscriber Identity Module Expert Group was a committee of specialists assembled by the European Telecommunications Standards Institute (ETSI) to draw up the specifications ([[GSM]] 11.11) for interfacing between smart cards and mobile telephones. In 1994, the name SIMEG was changed to SMG9.

Japan's current and next-generation cellular systems are based on W-CDMA (UMTS) and [[CDMA2000]] and all use SIM cards. However, Japanese CDMA2000-based phones are locked to the R-UIM they are associated with and thus, the cards are not interchangeable with other Japanese CDMA2000 handsets (though they may be inserted into GSM/WCDMA handsets for roaming purposes outside Japan).

[[Code-division multiple access|CDMA]]-based devices originally did not use a removable card, and the service for these phones is bound to a unique identifier contained in the handset itself. This is most prevalent in operators in the Americas. The first publication of the TIA-820 standard (also known as 3GPP2 C.S0023) in 2000 defined the Removable User Identity Module ([[Removable User Identity Module|R-UIM]]). Card-based CDMA devices are most prevalent in Asia.

The equivalent of a SIM in [[UMTS]] is called the universal integrated circuit card (UICC), which runs a USIM application. The UICC is still colloquially called a ''SIM card''.<ref>{{cite web |url=https://pages.nist.gov/mobile-threat-catalogue/background/mobile-attack-surface/communication-mechanisms.html |title=Communication · Mobile Threat Catalogue |website=[[National Institute of Standards and Technology]] |access-date=19 June 2021 |quote=...colloquially referred to as the Subscriber Identity Module (SIM) card, although current standards use the term Universal Integrated Circuit Card (UICC). |archive-date=20 May 2021 |archive-url=https://web.archive.org/web/20210520090152/https://pages.nist.gov/mobile-threat-catalogue/background/mobile-attack-surface/communication-mechanisms.html |url-status=live }}</ref>

== SIM and carriers ==
The SIM card introduced a new and significant business opportunity for [[mobile virtual network operator|{{abbr|MVNOs|mobile virtual network operators}}]] who lease capacity from one of the network operators rather than owning or operating a cellular telecoms network and only provide a SIM card to their customers. MVNOs first appeared in Denmark, Hong Kong, Finland and the UK. By 2011 they existed in over 50 countries, including most of Europe, the United States, Canada, Mexico, Australia and parts of Asia, and accounted for approximately 10% of all mobile phone subscribers around the world.<ref>{{Cite journal |last1=Kimiloglu |first1=Hande |last2=Ozturan |first2=Meltem |last3=Kutlu |first3=Birgul |date=2011 |title=Market Analysis for Mobile Virtual Network Operators (MVNOs): The Case of Turkey |url=https://www.academia.edu/2119707 |journal=International Journal of Business and Management |volume=6 |issue=6 |doi=10.5539/ijbm.v6n6p39 |issn=1833-8119 |access-date=31 October 2022 |archive-date=20 June 2023 |archive-url=https://web.archive.org/web/20230620184742/https://www.academia.edu/2119707 |url-status=live |doi-access=free }}</ref>

On some networks, the mobile phone is [[SIM lock|locked to its carrier SIM card]], meaning that the phone only works with SIM cards from the specific carrier. This is more common in markets where mobile phones are heavily subsidised by the carriers, and the business model depends on the customer staying with the service provider for a minimum term (typically 12, 18 or 24 months). SIM cards that are issued by providers with an associated contract, but where the carrier does not provide a mobile device (such as a mobile phone) are called ''SIM-only'' deals. Common examples are the GSM networks in the United States, Canada, Australia, and Poland. UK mobile networks ended SIM lock practices in December 2021. Many businesses offer the ability to remove the SIM lock from a phone, effectively making it possible to then use the phone on any network by inserting a different SIM card. Mostly, GSM and 3G mobile handsets can easily be unlocked and used on any suitable network with any SIM card.

In countries where the phones are not subsidised, e.g., India, Israel and Belgium, all phones are unlocked. Where the phone is not locked to its SIM card, the users can easily switch networks by simply replacing the SIM card of one network with that of another while using only one phone. This is typical, for example, among users who may want to optimise their carrier's traffic by different tariffs to different friends on different networks, or when travelling internationally.

In 2016, carriers started using the concept of automatic SIM reactivation<ref>{{cite press release | url=http://globenewswire.com/news-release/2016/11/03/886048/0/en/Gemalto-pioneers-SIM-Reactivation-solution-to-help-operators-seamlessly-reconnect-with-lapsed-prepaid-subscribers.html | title=Gemalto pioneers SIM reactivation | date=3 November 2016 | access-date=2016-11-03 | archive-date=4 November 2016 | archive-url=https://web.archive.org/web/20161104035829/http://globenewswire.com/news-release/2016/11/03/886048/0/en/Gemalto-pioneers-SIM-Reactivation-solution-to-help-operators-seamlessly-reconnect-with-lapsed-prepaid-subscribers.html | url-status=live }}</ref> whereby they let users reuse expired SIM cards instead of purchasing new ones when they wish to re-subscribe to that operator. This is particularly useful in countries where [[prepaid telephone call|prepaid calls]] dominate and where competition drives high [[churn rate]]s, as users had to return to a carrier shop to purchase a new SIM each time they wanted to churn back to an operator.

=== SIM-only ===
Commonly sold as a product by mobile [[telecommunications]] companies, "SIM-only" refers to a type of [[Legal liability|legally liability]] contract between a mobile network provider and a customer. The contract itself takes the form of a credit agreement and is subject to a credit check.

SIM-only contracts can be ''pre-pay'' - where the subscriber buys ''credit'' before use (often called pay as you go, abbreviated to PAYG), or ''post-pay'', where the subscriber pays in arrears, typically monthly.

Within a SIM-only contract, the mobile network provider supplies their customer with just one piece of hardware, a SIM card, which includes an agreed amount of network usage in exchange for a monthly payment. Network usage within a SIM-only contract can be measured in minutes, text, data or any combination of these. The duration of a SIM-only contract varies depending on the deal selected by the customer, but in the UK they are typically available over 1, 3, 6, 12 or 24-month periods.

SIM-only contracts differ from mobile phone contracts in that they do not include any hardware other than a SIM card. In terms of network usage, SIM-only is typically more cost-effective than other contracts because the provider does not charge more to offset the cost of a mobile device over the contract period. The short contract length is one of the key features of SIM-only{{snd}} made possible by the absence of a mobile device.

SIM-only is increasing in popularity very quickly.<ref>{{cite web|title=A nation addicted to smartphones|url=http://media.ofcom.org.uk/2011/08/04/a-nation-addicted-to-smartphones/|publisher=Ofcom|access-date=6 July 2016|archive-date=23 April 2014|archive-url=https://web.archive.org/web/20140423214425/http://media.ofcom.org.uk/2011/08/04/a-nation-addicted-to-smartphones/|url-status=live}}</ref> In 2010 pay monthly based mobile phone subscriptions grew from 41 percent to 49 percent of all UK mobile phone subscriptions.<ref>{{cite web|title=UK sales of SIM-only mobile contracts set a new record|url=http://thefonecast.com/Home/TabId/61/ArtMID/538/ArticleID/6219/UK-sales-of-SIM-only-mobile-contracts-set-a-new-record.aspx|publisher=The Fone Cast|access-date=29 October 2012|archive-date=25 February 2013|archive-url=https://web.archive.org/web/20130225052426/http://thefonecast.com/Home/TabId/61/ArtMID/538/ArticleID/6219/UK-sales-of-SIM-only-mobile-contracts-set-a-new-record.aspx|url-status=live}}</ref> According to German research company [[GfK]], 250,000 SIM-only mobile contracts were taken up in the UK during July 2012 alone, the highest figure since GfK began keeping records.

Increasing smartphone penetration combined with financial concerns is leading customers to save money by moving onto a SIM-only when their initial contract term is over.

== Multiple-SIM devices ==
{{Main|Dual SIM}}

[[File:Locale_RS6_Lenovo S650 SIM card slots.JPG|thumb|Dual SIM slots as shown on a [[Lenovo ]][[smartphone]]]]
[[Dual SIM]] devices have two SIM card slots for the use of two SIM cards, from one or multiple carriers. Multiple SIM devices are commonplace in developing markets such as in [[Africa]], [[East Asia]], [[South Asia]] and [[Southeast Asia]], where variable billing rates, network coverage and speed make it desirable for consumers to use multiple SIMs from competing networks. Dual-SIM phones are also useful to separate one's personal phone number from a business phone number, without having to carry multiple devices. Some devices, such as the [[BlackBerry KeyOne]], have dual-SIM variants; however, dual-SIM devices were not common in the US or Europe due to lack of demand. This has changed with more recent smartphones featuring either two SIM slots or a combination of a physical SIM slot and an eSIM.

== Thin SIM==
[[File:Locale_RS6_GPP SIM interposer.jpg|thumb|A GPP-branded SIM interposer used to circumvent network restrictions on carrier-locked handsets]]
A '''thin SIM''' (or '''overlay SIM''' or '''SIM overlay''') is a very thin device shaped like a SIM card, approximately 120 microns ({{frac|200}} inch) thick. It has contacts on its front and back. It is used by placing it on top of a regular SIM card. It provides its own functionality while passing through the functionality of the SIM card underneath. It can be used to bypass the mobile operating network and run custom applications, particularly on non-programmable cell phones.<ref>Archived at [https://ghostarchive.org/varchive/youtube/20211211/IbfG_KSlTD4 Ghostarchive]{{cbignore}} and the [https://web.archive.org/web/20180124132856/https://www.youtube.com/watch?v=IbfG_KSlTD4 Wayback Machine]{{cbignore}}: {{cite web|url=https://www.youtube.com/watch?v=IbfG_KSlTD4|title=Keynote by Ross Anderson at CCS 2016|last=CCS 2016|date=7 November 2016|via=YouTube}}{{cbignore}}</ref>

Its top surface is a connector that connects to the phone in place of the normal SIM. Its bottom surface is a connector that connects to the SIM in place of the phone. With electronics, it can modify signals in either direction, thus presenting a modified SIM to the phone, and/or presenting a modified phone to the SIM. (It is a similar concept to the [[Game Genie]], which connects between a game console and a game cartridge, creating a modified game).

In 2014, [[Equitel]], an MVNO operated by Kenya's [[Equity Bank Kenya Limited|Equity Bank]], announced its intention to begin issuing thin SIMs to customers, raising security concerns by competition, particularly concerning the safety of mobile money accounts. However, after months of security testing and legal hearings before the country's Parliamentary Committee on Energy, Information and Communications, the [[Communications Authority of Kenya]] (CAK) gave the bank the green light to roll out its thin SIM cards.<ref>{{cite web|url=https://www.zdnet.com/article/africas-new-thin-sim-cards-the-line-between-banks-and-telcos-just-got-thinner/|title=Africa's new thin SIM cards: The line between banks and telcos just got thinner – ZDNet|first=Hilary|last=Heuler|website=[[ZDNet]]|access-date=24 November 2018|archive-date=2 May 2019|archive-url=https://web.archive.org/web/20190502121008/https://www.zdnet.com/article/africas-new-thin-sim-cards-the-line-between-banks-and-telcos-just-got-thinner/|url-status=live}}</ref>

== See also ==
* [[Apple SIM]]
* [[GSM 03.48]]
* [[International Mobile Equipment Identity]] (IMEI)
* [[IP Multimedia Services Identity Module]] (ISIM)
* [[Mobile broadband]]
* [[Mobile equipment identifier]] (MEID)
* [[Mobile signature]]
* [[Multi-SIM card]]
* [[Regional lockout]]
* [[Phone cloning|SIM cloning]]
* [[SIM connector]]
* [[Single Wire Protocol]] (SWP)
* [[Tethering]]
* [[Transponder]]
* [[Unstructured Supplementary Service Data|GSM USSD codes]]{{snd}} Unstructured Supplementary Service Data: list of standard GSM codes for network and SIM related functions
* [[VMAC]]
* [[W-SIM]] (Willcom-SIM)

== References ==
{{Reflist|37em}}

== External links ==
{{Commons category|SIM cards}}
* [http://www.3gpp.org/ftp/specs/html-info/1111.htm GSM 11.11] – Specification of the Subscriber Identity Module-Mobile Equipment (SIM-ME) interface.
* [http://www.3gpp.org/ftp/specs/html-info/1114.htm GSM 11.14] – Specification of the SIM Application Toolkit for the Subscriber Identity Module-Mobile Equipment (SIM-ME) interface
* [http://www.3gpp.org/ftp/specs/html-info/0348.htm GSM 03.48] – Specification of the security mechanisms for SIM application toolkit
* [https://github.com/opentelecoms-org/gsm0348 GSM 03.48 Java API] – API and realization of [[GSM 03.48]] in Java
* [http://www.itu.int/rec/T-REC-E.118-200605-I/en ITU-T E.118] – The International Telecommunication Charge Card 2006 ITU-T

{{Mobile phones}}
{{Use dmy dates|date=December 2020}}

[[Category:German inventions]]
[[Category:Mobile phone standards]]
[[Category:Cryptographic hardware]]
[[Category:Smart cards]]
[[Category:Computer access control]]