Enhanced Small Disk Interface
Encyclopedia
Enhanced Small Disk Interface (ESDI) was a disk 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 generalizing the control bus such that more kinds of devices (such as removable disks and tape drive
s) 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 was popular 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 Mbit/s (as opposed to ST-506's top speed of 7.5 Mbit/s), and many high-end SCSI drives of the era were actually high-end ESDI drives with SCSI bridge
s integrated on the drive.
By 1990, SCSI had matured enough to handle high data rates and multiple types of drives, and ATA was quickly overtaking ST-506 in the desktop market. These two events made ESDI less and less important over time, and by the mid-1990s, ESDI was no longer in common use.
ST-506
The ST-506 was the first 5.25 inch hard disk drive. Introduced in 1980 by Seagate Technology , it stored up to 5 megabytes after formatting and cost $1500. The similar 10 MB ST-412 was introduced in late 1981. Both used MFM encoding...
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 generalizing the control bus such that more kinds of devices (such as removable disks and tape drive
Tape drive
A tape drive is a data storage device that reads and performs digital recording, writes data on a magnetic tape. Magnetic tape data storage is typically used for offline, archival data storage. Tape media generally has a favorable unit cost and long archival stability.A tape drive provides...
s) 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 was popular in the mid-to-late 1980s, when SCSI
SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
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 Mbit/s (as opposed to ST-506's top speed of 7.5 Mbit/s), and many high-end SCSI drives of the era were actually high-end ESDI drives with SCSI bridge
Bridge (disambiguation)
A bridge is a structure built so that a transportation route can cross above an obstacle.Bridge can also refer to:-Places:* Bridge, Kent, in Kent, England* Bridge, California, a former town in Fresno County...
s integrated on the drive.
By 1990, SCSI had matured enough to handle high data rates and multiple types of drives, and ATA was quickly overtaking ST-506 in the desktop market. These two events made ESDI less and less important over time, and by the mid-1990s, ESDI was no longer in common use.
Connector Pinouts
| GROUND | 1 | 2 | ~HD SLCT 3 |
| GROUND | 3 | 4 | ~HD SLCT 2 |
| GROUND | 5 | 6 | ~WRITE GATE |
| GROUND | 7 | 8 | ~CNFG/STATUS |
| GROUND | 9 | 10 | ~XFER ACK |
| GROUND | 11 | 12 | ~ATTENTION |
| GROUND | 13 | 14 | ~HD SLCT 0 |
| Key (no pin) | 15 | 16 | ~SECTOR |
| GROUND | 17 | 18 | ~HD SLCT 1 |
| GROUND | 19 | 20 | ~INDEX |
| GROUND | 21 | 22 | ~READY |
| GROUND | 23 | 24 | ~XFER REQ |
| GROUND | 25 | 26 | ~DRV SLCT 0 |
| GROUND | 27 | 28 | ~DRV SLCT 1 |
| GROUND | 29 | 30 | Reserved |
| GROUND | 31 | 32 | ~READ GATE |
| GROUND | 33 | 34 | ~CMD DATA |
| ~DRV SLCTD | 1 | 2 | ~SECTOR |
| ~CMD COMPL | 3 | 4 | ~ADDR MK EN |
| GROUND | 5 | 6 | GROUND |
| +WRITE CLK | 7 | 8 | -WRITE CLK |
| GROUND | 9 | 10 | +RD/REF CLK |
| -RD/REF CLK | 11 | 12 | GROUND |
| +NRZ WRITE | 13 | 14 | -NRZ WRITE |
| GROUND | 15 | 16 | GROUND |
| +NRZ READ | 17 | 18 | -NRZ READ |
| GROUND | 19 | 20 | ~INDEX |