The Free On-line Dictionary of Computing (30 December 2018):

Enhanced Small Disk Interface
ESDI

    (ESDI) An obsolete hard disk
   controller standard, first introduced by Maxtor in 1983,
   and intended to be the successor to the original
   ST-506/ST-412.  ESDI was faster and more reliable, but
   still could not compete with IDE and SCSI.

   EDSI used two cables: a 20-pin data cable to each drive and a
   single 34-pin control cable daisy chain with the controller
   at one end and a terminator at the other.  In PCs, it
   supported up to two drives at 1-2MB/s with drives up to 2GB.

   PC Guide
   (http://pcguide.com/ref/hdd/if/obsoESDI-c.html).

   (2003-08-01)