(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.