SCSI (Small Computer System Interface)

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 can connect a wide range of other devices, including scanners, and optical drives (CD, DVD, etc.). The SCSI standard contains definitions of command sets of specific peripheral device types; the presence of "unknown" as one of these types means that in theory it can be used to interface almost any device, but the standard is highly pragmatic and addressed toward commercial requirements.

SCSI is available in a variety of interfaces. The first, still very common, was parallel SCSI (also called SPI). It uses a parallel electrical bus design. The traditional SPI design is making a transition to Serial Attached SCSI (SAS), which switches to a serial point-to-point design but retains other aspects of the technology. iSCSI drops physical implementation entirely, and instead uses TCP/IP as a transport mechanism. Finally, many other interfaces which do not rely on complete SCSI standards still implement the SCSI command protocol.