Enhanced Small 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-412/506 interface. 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 drives) 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 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 bridges 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

+ 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

+ 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

Enhanced Small Disk Interface

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