Editing SCSI (section)

==History==

===Parallel interface===
[[File:Adaptec ACB-4000A SASI card.jpg|thumb|Adaptec ACB-4000A SASI card from 1985]]
SCSI is derived from the [[Shugart Associates]] System Interface (SASI),<ref name="glass198902">{{Cite magazine |last=Glass |first=Brett |date=February 1989 |title=Hard Disk Interfaces |url=https://archive.org/details/eu_BYTE-1989-02_OCR/page/n350/mode/1up?view=theater |access-date=2024-10-08 |magazine=BYTE |pages=293-297}}</ref> developed beginning 1979<ref>{{cite book
|title=Data Technology Corporation Prospectus |date=May 27, 1987 |quote=In 1979 the Company developed the first controller using the SASI interface ... in conjunction with Shugart Associates}}</ref> and publicly disclosed in 1981.<ref name="draft">ANSI Draft SASI Standard, Rev D, February 17, 1982, pg. ii states, "9/15/81 first presentation to ANSI committee X3T9-3 (2 weeks following announcement in Electronic Design)."</ref> [[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]], which he founded in 1981.<ref>{{cite book | last=Bahrami | first=Homa | author2=J. Stuart Evans | date=2005 | url=https://books.google.com/books?id=OlFUPUIcHoMC | title=Super-flexibility for Knowledge Enterprises | publisher=9783540205760 | page=59 | isbn=9783540205760 | via=Google Books}}</ref>

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.<ref>ANSI SCSI Standard, X3.131-1986, June 23, 1986, 2nd, foreword.</ref>

In around 1980, [[NCR Corporation]] had been developing a competing interface standard by the name of BYSE. In the summer of 1981, NCR abandoned their in-house efforts in favor of pursuing SASI and improving on its design for their own computer systems. Fearing that their extension of the SASI standard would induce market confusion, however, NCR briefly cancelled their contract with Shugart. NCR's proposed improvements to the design of SCSI piqued the interest of Optimem, a subsidiary of Shugart, who requested that NCR and Shugart collaborate on a unified standard. In October 1981, the two companies agreed to co-develop SASI and present their standard jointly with ANSI.<ref name=spt>{{cite book | last=Musumeci | first=Gian-Paolo D. | author2=Michael Kosta Loukides | date=2002 | url=https://books.google.com/books?id=LqabAgAAQBAJ | title=System Performance Tuning | publisher=O'Reilly Media | page=147 | isbn=9780596002848 | via=Google Books}}</ref><ref>{{cite book | last=O'Reilly | first=James | date=2016 | url=https://books.google.com/books?id=Vop4CgAAQBAJ | title=Network Storage: Tools and Technologies for Storing Your Company's Data | publisher=Elsevier Science | page=255 | isbn=9780128038659 | via=Google Books}}</ref>

Until at least February 1982, ANSI developed the specification as "SASI" and "Shugart Associates System Interface".<ref name="ANSI">Working document for ANSI meeting on March 3, 1982, "SASI SHUGART ASSOCIATES SYSTEM INTERFACE, Revision D, February 17, 1982"</ref> 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<ref>{{cite web|url=http://www.endl.com/ |title=ENDL Inc. Home Page |publisher=Endl.com |date=2014-04-27 |access-date=2014-05-11}}</ref> Dal Allan pronounced the new acronym as "scuzzy" and that stuck.<ref name="CHM">{{cite web|url=https://www.youtube.com/watch?v=OiLUIJ3ke-o | archive-url=https://ghostarchive.org/varchive/youtube/20211117/OiLUIJ3ke-o| archive-date=2021-11-17 | url-status=live|title="How Computer Storage Became a Modern Business", Computer History Museum, March 9, 2005 | date=December 7, 2007|publisher=Youtube.com |access-date=2014-05-11}}{{cbignore}}</ref>

The NCR facility in [[Wichita, Kansas]] developed the industry's first SCSI controller chip, the NCR 5385, released in 1983. According to its developers, the chip worked the first time it was tested.<ref>{{cite web|url=http://smithsonianchips.si.edu/ncr/scsi-1.htm |title=NCR Collection (LSI Logic)at Smithsonian Museum |publisher=Smithsonianchips.si.edu |access-date=2014-05-11}}</ref><ref>{{cite journal | last=Bursky | first=D. | date=April 28, 1983 | url=https://link.gale.com/apps/doc/A536889/GPS?sid=wikipedia | title=Single-Chip Controller Handles SCSI | journal=Electronic Design | publisher=Endeavor Business Media | volume=31 | issue=9 | page=268 | via=Gale | quote=NCR Corp., Microelectronics Division has announced the release of its NCR 5385 single-chip controller. NCR is the first to use the Small Computer System Interface (SCSI) protocol.}}</ref> A number of companies, such as Adaptec and Optimem, were early supporters of SCSI.<ref name="ANSI"/> By late 1990 at least 45 manufactures offered 251 models of [[parallel SCSI]] host adapters<ref>{{cite report |title=SCSI Source Guide |date= Fourth Quarter 1990 |publisher= Technology Forums Inc |section=SCSI Products - Host Bus Adapters |pages=195–260}}</ref> Today, such host adapters have largely been displaced by the faster serial SCSI (SAS) host adapters.<ref>{{cite web
 |url=https://www.techtarget.com/searchstorage/definition/host-bus-adapter |title=host bus adapter (HBA) |last1=Sheldon |first1=Robert |last2=Sliwa |first2= Carol
 |publisher=TechTarget |access-date=April 18, 2024}}</ref>

The "small" reference in "small computer system interface" 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]], [[Atari Corporation|Atari]], [[Apple Macintosh]] and [[Sun Microsystems]] computer lines and PC server systems. Apple started using the less-expensive [[parallel ATA]] (PATA, 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, while still offering a [[Conventional PCI|PCI]] SCSI host adapter as an option on up to the Power Macintosh G4 (AGP Graphics) models.<ref>{{cite web|url=http://support.apple.com/kb/HT3074?viewlocale=en_US |title=Power Macintosh G3, G4: Differences Between Available SCSI Cards |publisher=Apple, Inc.|date=2010-04-01 |access-date=2014-07-07}}</ref> Sun switched its lower-end range to [[Parallel ATA]] (PATA) with introduction of their [[Ultra 5/10|Ultra 5 and 10]] low end workstations using [[CMD640]] IDE controller and continued this trend with the later [[Sun Blade (workstation)|Blade 100 and 150]] entry level systems and did not switch to contemporary [[SATA]] interface even with the introduction of the Blade 1500 in 2003 while the higher end Blade 2500 released at the same time used Ultra320 Parallel SCSI-3. Sun moved to [[SATA]] and [[Serial Attached SCSI|SAS]] interfaces with their last UltraSPARC-III based workstations in 2006 with the entry level Ultra 25 and mid-range Ultra 45. Commodore included SCSI on the Amiga 3000/3000T systems and it was an add-on to previous Amiga 500/2000 models. Starting with the Amiga 600/1200/4000 systems Commodore switched to the IDE interface. Atari included SCSI as standard in its [[Atari MEGA STE]], [[Atari TT]] and [[Atari Falcon]] computer models. 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 [[RAID]]s became common in PC workstations for video or audio production.

==={{Anchor|SERIAL-VARIANTS}}Modern SCSI===
Recent physical versions of SCSI{{mdashb}}[[Serial Attached SCSI]] (SAS), SCSI-over-[[Fibre Channel Protocol]] (FCP), and [[USB Attached SCSI]] (UAS){{mdashb}}break from the traditional parallel SCSI bus and perform data transfer via serial communications using [[point-to-point (telecommunications)|point-to-point]] links. Although much of the SCSI documentation talks about the parallel interface, all modern development efforts use serial interfaces. Serial interfaces have a number of advantages over parallel SCSI, including higher data rates, simplified cabling, longer reach, improved fault isolation and [[full-duplex]] capability. 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.<ref>{{Cite web |url=http://www.infostor.com/index/articles/display/232832/articles/infostor/volume-9/issue-7/features/special-report/the-benefits-of-serial-attached-scsi-sas.html |title=The benefits of Serial Attached SCSI (SAS) |author=David Allen |date=2005-07-01 |access-date=2015-02-06}}</ref>

The non-physical [[iSCSI]] preserves the basic SCSI [[paradigm]], especially the command set, almost unchanged, through embedding of SCSI-3 over [[TCP/IP]]. Therefore, iSCSI uses ''logical connections'' instead of physical links and can run on top of any network supporting IP. The actual physical links are realized on lower [[OSI model|network layers]], independently from iSCSI. Predominantly, [[Ethernet]] is used which is also of serial nature.

SCSI is popular on high-performance workstations, servers, and storage appliances. Almost all RAID subsystems on servers have used some kind of SCSI hard disk drives for decades (initially Parallel SCSI, interim Fibre Channel, recently SAS), though a number of manufacturers offer [[SATA]]-based RAID subsystems as a cheaper option. Moreover, SAS offers compatibility with SATA devices, creating a much broader range of options for RAID subsystems together with the existence of [[nearline SAS]] (NL-SAS) drives. Instead of SCSI, modern desktop computers and notebooks typically use SATA interfaces for internal hard disk drives, with [[NVMe]] over PCIe gaining popularity as SATA can bottleneck modern [[solid-state drive]]s.