RS-485: Imported from Wikipedia (overwrite)

2026-05-02T18:05:33Z

Imported from Wikipedia (overwrite)

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{{Short description|Disk interface}}
'''Enhanced Small Disk Interface''' ('''ESDI''') is a [[hard disk drive interface]] designed by [[Maxtor Corporation]] in 1983 to be a follow-on to the [[ST-506|ST-412/506]] interface.<ref name="glass198902">{{Cite magazine |last=Glass |first=Brett |date=February 1989 |title=Hard Disk Interfaces |url=https://archive.org/details/eu_BYTE-1989-02_OCR/page/n350/mode/1up?view=theater |access-date=2024-10-08 |magazine=BYTE |pages=293-297}}</ref> ESDI improved on ST-506 by moving certain parts that were traditionally kept on the controller (such as the [[data separator]]) into the drives themselves, and also generalizing the control bus such that more kinds of devices (such as removable disks and [[tape drive]]s) could be connected. ESDI uses the same cabling as ST-506 (one 34-pin common control cable, and a 20-pin data channel cable for each device), and thus could easily be retrofitted to ST-506 applications.

ESDI was popular in the mid-to-late 1980s, when [[SCSI]] and [[Advanced Technology Attachment|IDE]] technologies were young and immature, and ST-506 was neither fast nor flexible enough. ESDI could handle data rates of 10, 15, or 20 Mbit/s (as opposed to ST-506's top speed of 7.5 Mbit/s), and many high-end SCSI drives of the era were actually high-end ESDI drives with SCSI [[Protocol_converter|bridge]]s integrated on the drive.

By 1990, SCSI had matured enough to handle high data rates and multiple types of drives, and ATA was quickly overtaking ST-506 in the desktop market. These two events made ESDI less and less important over time, and by the mid-1990s, ESDI was no longer in common use.

==Connector pinouts==

{| class="wikitable"
|+ ESDI 34-pin control connector pinout
|-
| GROUND || 1 || 2 || ~HD SLCT 3
|-
| GROUND || 3 || 4 || ~HD SLCT 2
|-
| GROUND || 5 || 6 || ~WRITE GATE
|-
| GROUND || 7 || 8 || ~CNFG/STATUS
|-
| GROUND || 9 || 10 || ~XFER ACK
|-
| GROUND || 11 || 12 || ~ATTENTION
|-
| GROUND || 13 || 14 || ~HD SLCT 0
|-
| Key (no pin) || 15 || 16 || ~SECTOR
|-
| GROUND || 17 || 18 || ~HD SLCT 1
|-
| GROUND || 19 || 20 || ~INDEX
|-
| GROUND || 21 || 22 || ~READY
|-
| GROUND || 23 || 24 || ~XFER REQ
|-
| GROUND || 25 || 26 || ~DRV SLCT 0
|-
| GROUND || 27 || 28 || ~DRV SLCT 1
|-
| GROUND || 29 || 30 || Reserved
|-
| GROUND || 31 || 32 || ~READ GATE
|-
| GROUND || 33 || 34 || ~CMD DATA
|}

{| class="wikitable"
|+ ESDI 20-pin data connector pinout
|-
| ~DRV SLCTD || 1 || 2 || ~SECTOR
|-
| ~CMD COMPL || 3 || 4 || ~ADDR MK EN
|-
| GROUND || 5 || 6 || GROUND
|-
| +WRITE CLK || 7 || 8 || −WRITE CLK
|-
| GROUND || 9 || 10 || +RD/REF CLK
|-
| −RD/REF CLK || 11 || 12 || GROUND
|-
| +NRZ WRITE || 13 || 14 || −NRZ WRITE
|-
| GROUND || 15 || 16 || GROUND
|-
| +NRZ READ || 17 || 18 || −NRZ READ
|-
| GROUND || 19 || 20 || ~INDEX
|}

==References==
{{refbegin}}
* [http://www.bitsavers.org/pdf/micropolis/ESDI_spec_X3.170-90.pdf Micropolis ESDI X3.170-90 Interface Specification]
* [http://www.bitsavers.org/pdf/cdc/discs/wren/77738076D2_CDC_ESDI_Specification_Nov84.pdf ESDI Specification, Magnetic Peripherals Inc, 1984]
* [http://www.mcamafia.de/pdf/ibm_esdi_trm.pdf IBM ESDI Fixed Disk Drive Adapter/A Technical Reference]
{{refend}}

{{Computer-bus}}

[[Category:Computer storage buses]]

Enhanced Small Disk Interface - Revision history

RS-485: Imported from Wikipedia (overwrite)