IBM 90X8528 ESDI 70MB Hard Drive Spinning Up

Enhanced Small Disk Interface (ESDI) was a disc interface designed by Maxtor Corporation in the early 1980s to be a follow-on to the ST-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 generalising the control bus such that more kinds of devices (such as removable disks and tape drives) could be connected. ESDI used 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 enjoyed popularity in the mid-to-late 1980s, when SCSI and ATA were young and immature, and ST-506 was not fast or flexible enough. ESDI could handle data rates of 10, 15, or 20 megabits per second (as opposed to ST-506’s top speed of 7.5 megabits), and many high-end SCSI drives of the era were actually high-end ESDI drives with SCSI bridges integrated on the drive.