Enhanced Small Disk Interface

Enhanced Small Disk Interface (ESDI) is a <a href="/facts/Hard_disk_drive_interface/gfy8Qgaj">hard disk drive interface</a> designed by <a href="/facts/Maxtor_Corporation/GYHKwDod">Maxtor Corporation</a> in 1983 to be a follow-on to the <a href="/facts/ST-506/AzNuWd63">ST-412/506</a> interface. ESDI improved on ST-506 by moving certain parts that were traditionally kept on the controller (such as the <a href="/facts/Data_separator/XLIItN1f">data separator</a>) into the drives themselves, and also generalizing the control bus such that more kinds of devices (such as removable disks and <a href="/facts/Tape_drive/9MfLuCa0">tape drives</a>) 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 <a href="/facts/SCSI/pxXulrBr">SCSI</a> and <a href="/facts/Advanced_Technology_Attachment/QPchqXH8">IDE</a> 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 <a href="/facts/Protocol_converter/49C9D667">bridges</a> 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.

Enhanced Small Disk Interface open-in-new

Enhanced Small Disk Interface