Small Computer System Interface (
SCSI, ) is a set of standards for physically connecting and transferring data between computers and
peripheral devices. The SCSI standards define
commands, protocols, electrical and optical
interfaces. SCSI is most commonly used for
hard disk drives and
tape drives, but it can connect a wide range of other devices, including scanners and
CD drives, although not all controllers can handle all devices. The SCSI standard defines command sets for specific
peripheral device types; the presence of "unknown" as one of these types means that in theory it can be used as an interface to almost any device, but the standard is highly pragmatic and addressed toward commercial requirements.