SCSI - History

History

SCSI was derived from "SASI", the "Shugart Associates System Interface", developed c. 1978 and publicly disclosed in 1981. 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.

Larry Boucher is considered to be the "father" of SASI and SCSI due to his pioneering work first at Shugart Associates and then at Adaptec.

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 the SCSI standard. The NCR facility in Wichita, Kansas is widely thought to have developed the industry's first SCSI chip; it worked the first time.

The "small" part in SCSI is historical; since the mid-1990s, SCSI has been available on even the largest of computer systems.

Since its standardization in 1986, SCSI has been commonly used in the Amiga, Apple Macintosh and Sun Microsystems computer lines and PC server systems. Apple started using Parallel ATA (also known as IDE) for its low-end machines with the Macintosh Quadra 630 in 1994, and added it to its high-end desktops starting with the Power Macintosh G3 in 1997. Apple dropped on-board SCSI completely (in favor of IDE and FireWire) with the (Blue & White) Power Mac G3 in 1999. Sun has switched its lower end range to Serial ATA (SATA). SCSI has never been popular in the low-priced IBM PC world, owing to the lower cost and adequate performance of ATA hard disk standard. However, SCSI drives and even SCSI RAIDs became common in PC workstations for video or audio production.

Recent versions of SCSI – Serial Storage Architecture (SSA), SCSI-over-Fibre Channel Protocol (FCP), Serial Attached SCSI (SAS), Automation/Drive Interface − Transport Protocol (ADT), and USB Attached SCSI (UAS) – break from the traditional parallel SCSI standards and perform data transfer via serial communications. Although much of the documentation of SCSI talks about the parallel interface, most contemporary development effort is on serial SCSI. Serial SCSI has a number of advantages over parallel SCSI: faster data rates, hot swapping (some but not all parallel SCSI interfaces support it), and improved fault isolation. The primary reason for the shift to serial interfaces is the clock skew issue of high speed parallel interfaces, which makes the faster variants of parallel SCSI susceptible to problems caused by cabling and termination.

iSCSI preserves the basic SCSI paradigm, especially the command set, almost unchanged, through embedding of SCSI-3 over TCP/IP.

SCSI is popular on high-performance workstations and servers. RAIDs on servers have almost always used SCSI hard disks, though a number of manufacturers now offer SATA-based RAID systems as a cheaper option. Instead of SCSI, desktop computers and notebooks more typically use ATA interfaces for internal hard disk drives, and USB, eSATA, and FireWire connections for external devices.

As of 2012 SCSI interfaces had become impossible to find for laptop computers. Adaptec had years before produced PCMCIA SCSI interfaces, but when PCMCIA was superseded by the ExpressCard discontinued their PCMCIA line without supporting ExpressCard. Ratoc produced USB and Firewire to SCSI adaptors, but ceased production when the integrated circuits required were discontinued. Drivers for existing PCMCIA interfaces were not produced for newer operating systems.