The first attempt at improving the original ST-506/ST-412 hard disk interface was the Enhanced
Small Device Interface or ESDI. ESDI was developed in the mid-1980s by a
consortium of hard disk manufacturers led by Maxtor. It was eventually codified as an ANSI
standard; the peak of its popularity was in the late 1980s.
ESDI improved on ST-506/ST-412 in several ways. It moved some drive controller
functions to the hard disk from the controller card, eliminating some of the reliability
problems associated with its predecessor. It had a maximum theoretical bandwidth of 24
Mbits/second (fairly fast for those days), though in practice the limit was about half of
that. There were other added features and small performance enhancements as well. Its
primary design still had almost all of the intelligence on the controller and not on the
hard disk.
While ESDI was a real improvement over the older ST-506/ST-412 interface, it was
"too little, too late" in a lot of ways. In the late 1980s ESDI suffered under
competition from IDE/ATA in the mainstream market and from SCSI in the high-end market,
both of which offered significant advantages over ESDI, such as simpler configuration,
lower cost and improved performance. As a result, by the early 1990s ESDI had been all but
wiped off the interface map.
Next: Specialty and Future Hard Disk Interfaces
