The Small Computer Systems Interface is a type of computer system bus designed for high-speed parallel communication. It is most frequently used for setting up redundant arrays of inexpensive hard disk drives (RAID arrays). SCSI can support multipe devices per channel, unlike IDE--another bus that allows computers to communicate with disk drives.
There are several versions of SCSI that were developed over time to fit various needs (usually, the need for increased speed).
| SCSI Type | Bus | Connector | Speed |
|---|---|---|---|
| SCSI-1 | 8-bit | 25-pin | 4 MBps |
| SCSI-2 | 50-pin | ||
| SCSI Wide | 16-bit | 168-pin | |
| SCSI Fast | 8-bit | 10MBps | |
| SCSI Fast-Wide | 16-bit | 20 MBps | |
| Ultra SCSI | 8-bit | ||
| SCSI-3 (Ultra-Wide) | 16-bit | ||
| Ultra2 SCSI | 40 MBps | ||
| Wide Ultra2 SCSI | 16-bit | 80 MBps | |
- Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers.
- Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10 MBps.
- Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MBps.
- Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MBps.
- SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps. Also called Ultra Wide SCSI.
- Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps.
- Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MBps.
- Serial Attached SCSI (SAS): Uses same pinout as SATA
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