ESDI (Enhanced Small Disk Interface)
A faster successor to ST-506 that moved the encoding onto the drive and added a proper command set.
A Maxtor-led industry group defined the interface around 1983. By serializing and encoding the data on the drive itself and sending it already decoded over the cable, ESDI reached 10–24 Mbit/s against ST-506's 5–7.5. A defined command set also let the host ask the drive about its own geometry instead of having it typed in by hand.
ESDI was a bridge between the dumb ST-506 and the intelligent SCSI and IDE. The bridge proved short-lived: by the early 1990s IDE had taken the desktop and SCSI the servers, and ESDI fell away.