Small Computer System Interface

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The Small Computer System Interface (universally known by its acronym, SCSI) was a popular interface standard for high-speed devices (disks, tape drives, scanners, etc). It was composed of a set of standards for the various layers: physical signalling, commands, etc.

Over time, a variety of options were developed for many of these; e.g. the original standard was 8-bit parallel using single-ended signalling, but later versions used 16-bit with differential pairs, at a variety of speeds (mostly synchronous, but one was asynchronous). Even later, a high-speed serial version was developed; and ultimately, one which worked over TCP/IP (usually over an Ethernet).

SCSI Versions

Some common SCSI Versions
Name Alternative Name max. Devices Bus Bandwidth MB/sec
Fast(-Narrow) SCSI (Narrow) SCSI-2 8 10
Fast-Wide SCSI (Wide) SCSI-2 16 20
Ultra(-Wide) SCSI (Wide) SCSI-3 16 40