The Small Computer Systems Interface started as a high data-rate, general-purpose parallel interface introduced in 1979 allowing up to eight devices to be connected to one bus (now 16 for Wide SCSI). This could comprise a controller and up to seven disks or devices of different sorts – hard disks, optical disks, tape drives, scanners, etc., and may be shared between several computers.

Since then SCSI has hugely increased in performance but is now used mainly on high-performance workstations and RAIDs on servers while other lower cost interfaces such as USB2 and IEEE1394 connect external devices, while SATA is used for many hard disks.

The original SCSI specified a cabling standard (50-way) that had to be kept short, a protocol for sending and receiving commands and their format. It is intended as a device-independent interface so the host computer needs no details about the peripherals it controls. SCSI’s continued development has resulted in ever faster data transfer rates. Currently 16GFC (Fibre Channel) has a maximum transfer rate of 1600 MB/s (12.6 Gb/s).

There are many other SCSI interfaces besides Fibre Channel. iSCSI (Internet Small Computer System Interface) can run over any physical transport capable of transporting Internet Protocol (IP). This gets much support as developments in Ethernet outpace those in FC. The performance of this though is network-dependent.

Serial SCSI using SSA (Serial Storage Architecture) FC-AL, IEEE1394, and Serial Attached SCSI (SAS), break away from the parallel cabling to offer data transfers currently up to 1200 MB/s. This is popular with many hard disk drives.

See also: Disk drives