SCSI

Small Computer System Interface (SCSI, /ˈskʌzi/ SKUZ-ee) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical 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. The ancestral SCSI standard, X3.131-1986, generally referred to as SCSI-1, was published by the X3T9 technical committee of the American National Standards Institute (ANSI) in 1986. SCSI-2 was published in August 1990 as X3.T9.2/86-109, with further revisions in 1994 and subsequent adoption of a multitude of interfaces. Further refinements have resulted in improvements in performance and support for ever-increasing storage data capacity. SCSI is derived from 'SASI', the 'Shugart Associates System Interface', developed circa 1978 and publicly disclosed in 1981. Larry Boucher is considered to be the 'father' of SASI and ultimately SCSI due to his pioneering work first at Shugart Associates and then at Adaptec. A SASI controller provided a bridge between a hard disk drive's low-level interface and a host computer, which needed to read blocks of data. SASI controller boards were typically the size of a hard disk drive and were usually physically mounted to the drive's chassis. SASI, which was used in mini- and early microcomputers, defined the interface as using a 50-pin flat ribbon connector which was adopted as the SCSI-1 connector. SASI is a fully compliant subset of SCSI-1 so that many, if not all, of the then-existing SASI controllers were SCSI-1 compatible. Until at least February 1982, ANSI developed the specification as 'SASI' and 'Shugart Associates System Interface;' however, the committee documenting the standard would not allow it to be named after a company. Almost a full day was devoted to agreeing to name the standard 'Small Computer System Interface', which Boucher intended to be pronounced 'sexy', but ENDL's Dal Allan pronounced the new acronym as 'scuzzy' and that stuck. A number of companies such as NCR Corporation, Adaptec and Optimem were early supporters of SCSI. The NCR facility in Wichita, Kansas is widely thought to have developed the industry's first SCSI controller chip; it worked the first time.