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{{Short description|Computer bus standard}}
{{hatnote|"Multibus" is also an early name for a [[bus]], a passenger vehicle.}}
[[File:Locale_RS6_Sun2 CPU.jpg|thumb|Multibus I CPU card from a Sun-2 workstation]]
[[Image:Intel iSBC 386 116 Multibus II Single Bus Computer.JPG|thumb|Intel iSBC 386/116 Multibus II Single Board Computer with [[VLSI Technology|VLSI]] A82389 as Multibus Controller]]
'''Multibus''' is a [[computer bus]] standard used in industrial systems. It was developed by [[Intel|Intel Corporation]] and was adopted as the [[Institute of Electrical and Electronics Engineers|IEEE]] 796 bus.<ref>{{cite book|title=IEEE Standard Microcomputer System Bus |date=December 1983 |pages=1–46 |publisher=[[IEEE]] |doi=10.1109/IEEESTD.1983.81701 |isbn=978-0-7381-2753-8 }}</ref>

The Multibus specification was a robust industry standard with a relatively large form factor, allowing complex devices to be designed on it. Because it was well-defined and well-documented, a Multibus-compatible industry grew around it, with many companies making card cages and enclosures for it. Many others made [[CPU]], memory, and other peripheral boards. In 1982, there were over 100 Multibus board and systems manufacturers.<ref>{{Cite FTP |url=ftp://reports.stanford.edu/pub/cstr/reports/csl/tr/82/229/CSL-TR-82-229.pdf |server=reports.stanford.edu |url-status=dead |title=FTP link }}The SUN Workstation Architecture, Andreas Bechtolsheim, Forest Baskett, Vaughan Pratt, Stanford University Computer systems Laboratory Technical Report No. 229, March 1982</ref> This allowed complex systems to be built from [[commercial off-the-shelf]] hardware, and also allowed companies to innovate by designing a proprietary Multibus board, then integrate it with another vendor's hardware to create a complete system.

One example of this was [[Sun Microsystems]] with their [[Sun-1]] and [[Sun-2]] workstations. Sun built custom-designed CPU, memory, [[SCSI]], and video display boards, and then added [[3Com]] [[Ethernet]] networking boards, [[Xylogics]] SMD [[disk controller]]s, Ciprico Tapemaster 1/2 inch tape controllers, Sky [[Floating Point Unit|Floating Point Processor]], and Systech 16-port Terminal Interfaces in order to configure the system as a [[workstation]] or a [[file server]].<ref>[http://www.math.ucdavis.edu/~zjohnson/doc/sun_hw_faq.html The Sun Hardware Reference] {{webarchive |url=https://web.archive.org/web/20070102133425/http://www.math.ucdavis.edu/~zjohnson/doc/sun_hw_faq.html |date=January 2, 2007 }}</ref> Other workstation vendors who used Multibus-based designs included [[Hewlett-Packard|HP]]/[[Apollo Computer|Apollo]]<ref>{{cite web |url=http://www.umich.edu/~archive/apollo/partnos.txt |title=Archived copy |access-date=2008-04-25 |url-status=dead |archive-url=https://web.archive.org/web/20100608085434/http://www.umich.edu/~archive/apollo/partnos.txt |archive-date=2010-06-08 }} HP/APOLLO SYSTEMS INFORMATION</ref> and [[Silicon Graphics]].<ref>http://www.futuretech.blinkenlights.nl/iris-faq.html {{Webarchive|url=https://web.archive.org/web/20130904132640/http://www.futuretech.blinkenlights.nl/iris-faq.html |date=2013-09-04 }} Silicon Graphics IRIS 2000/3000 FAQ</ref>

The Intel Multibus I & II product line was purchased from Intel by [[RadiSys Corporation]], which in 2002 was then purchased by [http://www.ustechnologies.com U.S. Technologies, Inc.]

== Multibus architecture ==
Multibus was an [[Asynchronous I/O|asynchronous]] bus that accommodated devices with various transfer rates while maintaining a maximum [[throughput]]. It had 20 address lines so it could address up to 1 [[Megabit|Mb]] of Multibus memory and 1 Mb of I/O locations. Most Multibus I/O devices only decoded the first 64 Kb of address space.

Multibus supported [[Multi-master bus|multi-master]] functionality that allowed it to share the Multibus with multiple processors and other [[Direct memory access|DMA]] devices.<ref>Sun 68000 Board User's Manual, Sun Microsystems, Inc, February 1983, Revision B</ref>

The standard Multibus form factor was a {{convert|12|in|mm|adj=mid|-wide}}, {{convert|6.75|in|mm|adj=mid|-deep}} circuit board with two ejection levers on the front edge. The board had two buses: a wider P1 bus with pin assignment defined by the Multibus specification and a second smaller P2 bus was also defined as a private bus.

==Multibus standards==
Multibus includes the following buses:
* Multibus System Bus — adopted as IEEE 796
* iSBX (I/O Expansion Bus) — adopted as IEEE P959
* iLBX [[local bus|Local Bus]] Extension<ref>[http://dl.acm.org/citation.cfm?id=1500738 AFIPS '83 Proceedings of the May 16-19, 1983, national computer conference], Pages 497-501. ACM digital library</ref> (Execution Bus)
* Multichannel I/O Bus

==Versions==
===Multibus I===
IEEE-796: Microcomputer System Bus; First released by Intel in 1974. The cards did not use front panels, instead using card edge fingers as the connectors (similar to ISA/PC-AT cards). Companies like Northwest Technical still provide "End of Life" products for Multibus I, which is now considered obsolete. The following are a list sections relevant to Multibus from the IEC 796 standard:
*IEC 796-1:1990 Microprocessor system bus—8-bit and 16-bit data (Multibus I) — Part 1: Functional description with electrical and timing specifications
*IEC 796-2:1990 Microprocessor system bus—8-bit and 16-bit data (Multibus I) — Part 2: Mechanical and pin descriptions for the system bus configuration, with edge connectors (direct)
*IEC 796-3:1990 Microprocessor system BUS I, 8-bit and 16-bit data (Multibus I) — Part 3: Mechanical and pin descriptions for the Eurocard configuration with pin and socket (indirect) connectors

===Multibus II===
IEEE-1296 32-bit/10 MHz bus, at 40 Mbyte/s. Card sizes are 3U x 220 mm, and 6U x 220 mm. These cards are larger than the VME Eurocard sizes, which are 3U/6U x 160mm. It uses TTL ("Fast" series) gates for drivers and the Backplane Connectors are [[DIN 41612]] type C. Multibus II is not yet considered obsolete, but considered mature; however it is not recommended for new designs. IEEE-STD-1296: High-performance synchronous 32-bit bus: Multibus II, released in 1987, and 1994. Also as ISO/IEC 10861.
*ISO/IEC 10861:1994 Information technology—Microprocessor systems—High-performance synchronous 32-bit bus: Multibus II

==Historical uses==
{{refimprove|section|date=August 2014}}
Multibus-II hardware running the [[iRMX]] operating system is used in the majority of the core Automatic Train Supervision subsystems on CLSCS, the [[London Underground]] [[Central line (London Underground)|Central line]] Signals Control System. This was supplied by [[Westinghouse Rail Systems]] and commissioned from the mid-1990s. The Central line is an [[Automatic Train Operation]] line. The Automatic Train Supervision elements use a mixture of iRMX on Multibus, and [[Solaris (operating system)|Solaris]] on [[SPARC]] computers. Sixteen Multibus-based Local Site Computers are distributed along the line together with six central Multibus-based subsystems in the control centre. [[Real-time computing|Real time]] control and communications functions are provided by the Multibus-based processors and Sun workstations provide database functions and the operator consoles in the control room. All subsystem computers are [[Redundancy (engineering)|dual redundant]]. The [[safety-critical]] [[Automatic Train Protection]] component is provided by trackside and trainborne equipment that does not use Multibus. The system was still in full operation {{as of|2011|lc=yes}}. In the control centre, Westinghouse also provided a cut-down mimic of the system for staff training and software test purposes using much of the same hardware and software as the full ATS system, but connected to a computer (also Multibus-II and Sun based) to simulate train movements and signaling behavior.

[[Oslo Metro]] or Oslo Tunnelbane uses a similar (although less complex) Westinghouse-supplied Multibus hardware control system through the central [[Common Tunnel]] or Fellestunnelen tracks, but was expected to be decommissioned in 2011.

== See also ==
* [[S-100 bus]]
* [[VMEbus]]

==References==
{{Reflist}}

==External links==
* [https://web.archive.org/web/20050524071024/http://www.techfest.com/hardware/bus/multibus_sokos.htm Mark Sokos' Multibus I Description]
* [http://bitsavers.trailing-edge.com/pdf/intel/system3xx/173202-001_310sysIntr_Oct83.pdf Introduction to the System 310 Microcomputer], Intel Corporation (1983). Multibus-based system.
* [http://bitsavers.trailing-edge.com/pdf/intel/_busSpec/9800683D_Intel_Multibus_Specification_Jun82.pdf Intel Multibus Specification], Intel Corporation (1982).
* [http://www.textfiles.com/bitsavers/pdf/intel/_busSpec/145695revA_iLBXspec_Jan83.pdf Intel iLBX Bus Specification], Intel Corporation (1983).
* [https://web.archive.org/web/20120526073313/http://www.ustechnologies.com/products/multibus.cfm US Technologies official Multibus site]

{{Computer bus|state=uncollapsed}}
{{ISO standards}}

[[Category:Computer buses]]
[[Category:Intel]]

Multibus - Revision history

RS-485: Imported from Wikipedia (overwrite)