Enhanced Small Disk Interface


Enhanced Small Disk Interface was a disk interface designed by Maxtor Corporation in the early 1980s 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 into the drives themselves, and also generalizing the control bus such that more kinds of devices could be connected. ESDI used the same cabling as ST-506, 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, 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

GROUND12~HD SLCT 3
GROUND34~HD SLCT 2
GROUND56~WRITE GATE
GROUND78~CNFG/STATUS
GROUND910~XFER ACK
GROUND1112~ATTENTION
GROUND1314~HD SLCT 0
Key 1516~SECTOR
GROUND1718~HD SLCT 1
GROUND1920~INDEX
GROUND2122~READY
GROUND2324~XFER REQ
GROUND2526~DRV SLCT 0
GROUND2728~DRV SLCT 1
GROUND2930Reserved
GROUND3132~READ GATE
GROUND3334~CMD DATA

~DRV SLCTD12~SECTOR
~CMD COMPL34~ADDR MK EN
GROUND56GROUND
+WRITE CLK78-WRITE CLK
GROUND910+RD/REF CLK
-RD/REF CLK1112GROUND
+NRZ WRITE1314-NRZ WRITE
GROUND1516GROUND
+NRZ READ1718-NRZ READ
GROUND1920~INDEX