SCSI

Definition: SCSI

SCSI

Noun

1. Interface consisting of a standard port between a computer and its peripherals that is used in some computers.

"SCSI" is a common misspelling or typo for: sacs, ski, skis.

Domain	Definitions
Computing	SCSI n. [Small Computer System Interface] A bus-independent standard for system-level interfacing between a computer and intelligent devices. Typically annotated in literature with `sexy' (/sek'see/), `sissy' (/sis'ee/), and `scuzzy' (/skuh'zee/) as pronunciation guides -- the last being the overwhelmingly predominant form, much to the dismay of the designers and their marketing people. One can usually assume that a person who pronounces it /S-C-S-I/ is clueless. Source: Jargon File.
Census	(Small Computer System Interface) An interface standard for a personal computer that connects up to seven peripheral devices. SCSI is standard on the Macintosh series. (references)
Source: compiled by the editor from various references; see credits.

SCSI (pronouned "scuzzy", sometimes like "sexy"), stands for "Small Computer System Interface", and provides a standard means for transferring data between devices on a computer bus.

Shugart Technology (the company formed by storage wizard Alan Shugart after he left Shugart Associates) introduced SCSI in 1979, and initially referred to it as SASI (Shugart Associates System Interface). After a number of other companies (NCR being the first, in 1981) decided to adopt SASI, SASI received the new name "SCSI." NCR also helped start the standards process the next year, and in 1986, ANSI approved the SCSI spec (as X3.131-1986). Since then, SCSI has developed as an industry-wide standard, capable of being applied to virtually any computer system (there were even SCSI implementations for the venerable Commodore 64 home computer).

To attach a computer to the host bus requires a SCSI host adapter which controls the data transfer on the SCSI bus; the peripheral side must feature a SCSI controller (the SCSI controller is generally embedded -- integral to the peripheral -- in all but the earliest SCSI devices). SCSI is most commonly used for hard disks and tape storage devices, but also connects a wide range of other devices, including scanners, CD-ROM drives, CD writerss, and DVD drives. In fact, the entire SCSI standard promotes device independence, which means that theoretically anything can be made SCSI (SCSI printers actually exist).

SCSI has evolved over the years. The standards (in chronological order) are as follows:

SCSI-1: The original standard that was derived from SASI and formally adopted in 1986 by ANSI. SCSI-1 features an 8 bit bus (with parity), running asychronously at 3.5 MB/s or 5 MB/s in synchronous mode, and a maximum bus cable length of 6 meters (a little more than 18 feet -- compare that to the 18 inch (1.5 meter) limit of the ATA interface). A variation on the original standard included a high voltage differential (HVD) implementation whose maximum cable length was many times that of the single-ended version.
SCSI-2: This standard was introduced in 1989 and gave rise to the Fast SCSI and Wide SCSI variants. Fast SCSI doubled the maximum transfer rate to 10 MB/s and Wide SCSI doubled the bus width to 16 bits on top of that (to reach 20 MB/s). However, these improvements came at the minor cost of a reduced maximum cable length to 3 meters. SCSI-2 also specified a 32-bit version of Wide SCSI, which used 2 16-bit cables per bus; this was largely ignored by SCSI device makers, and was officially retired in SCSI-3.
SCSI-3: Also known as Ultra SCSI and fast-20 SCSI, it was introduced in 1992. The bus speed doubled again to 20 MB/s for "narrow" (8 bit) systems and 40 MB/s for wide. The maximum cable length stayed at 3 meters but ultra SCSI developed an undeserved reputation for extreme sensitivity to cable length and condition (faulty cables, connectors or terminators were often to blame for instability problems). SCSI-3 actually encompasses a plethora of protocol standards including serial transfer techniques like IEEE-1394 (Apple Computer's FireWire standard), fiber optic protocols, etc, that transmit data serially at a very rapid rate.
Ultra-2 SCSI: This standard was introduced c. 1997 and featured a low voltage differential (LVD) bus. For this reason ultra-2 is sometimes referred to as "LVD SCSI." Using LVD technology, it became possible to allow a maximum bus cable length of 12 meters (more than 36 feet!), with much greater noise immunity. At the same time, the data transfer rate was increased to 80 MB/s. Ultra-2 SCSI actually had a relatively short lifespan, as it was soon superseded by ultra-3 (ultra-160) SCSI.
Ultra-3 SCSI: Also known as ultra-160 SCSI and introduced toward the end of 1999, this version was basically an improvement on the ultra-2 standard, in that the transfer rate was doubled once more to 160 MB/s by the use of double transition clocking. Ultra-160 SCSI offered new features like cyclic redundancy check (CRC, an error correcting process) and domain validation.
Ultra-320: This is the ultra-160 standard with the data transfer rate doubled to 320 MB/s. Nearly all new SCSI hard drives being manufactured at the time of this writing (October 2003) are actually ultra-320 devices.
Ultra-640: Ultra-640 (otherwise known as fast-320) was promulgated as a standard (INCITS 367-2003 or SPI-5) in early 2003. Ultra-640 doubles the interface speed yet again, this time to 640 MB/s.

Note: Ultra-2, ultra-160 and ultra-320 devices may be freely mixed on the LVD bus with no compromise in performance, as the host adapter will negotiate the operating speed and bus management requirements for each device. Single-ended devices should not be attached to the LVD bus, as doing so will force all devices to run at the slower single-ended speed. Support for single-ended interfaces has been deprecated in the SPI-5 standard (which describes Ultra-640), so future devices may not be electrically backward compatible.

SCSI devices are generally backward-compatible, i.e., it is possible to connect a ultra-3 SCSI hard disk to a ultra-2 SCSI controller and use it (though with reduced speed and feature set).

Each SCSI device (including the computer's [host adapter]) must be configured to have a unique SCSI ID on the bus. Also, the SCSI bus must be terminated with a terminator. Both active and passive terminators are in common use, with the active type much preferred (and required on LVD buses). Improper termination is a common problem with SCSI installations.

It is possible to convert a wide bus to a narrow one, with wide devices closer to the adapter. To do this properly requires a cable which terminates the wide part of the bus. This is sometimes referred to as a cable with high-9 termination. Specific commands allow the host to determine the active width of the bus. This arrangement is discouraged.

In the past, SCSI was very popular on all kinds of computers. SCSI remains popular on high-performance workstations, servers, and high-end peripherals. Desktop computers and notebooks more typically use the slower ATA/IDE interfaces for hard disks and USB (USB uses the SCSI command set for some operations) for other devices, since these interfaces, although less general-purpose, cost less to implement.

The original SCSI standards specified the physical characteritics of the bus(es) and the electrical signalling sequences required to achieve a given action, as well as the command set that defines the different things SCSI devices can do. However, the SCSI command set itself is useful on its own, since it is mature and has a large body of knowledgeable users and designers. Therefore, partial uses of only the command set portion of SCSI have appeared. Fibre Channel, Serial Storage Architecture, InfiniBand, iScsi, USB, IEEE 1394 and Serial Attached Scsi are all use the Scsi command set for some operations.

Some observers expect the iSCSI standard, an embedding of SCSI-3 over TCP/IP, to replace Fibre Channel in the long run, as Ethernet data rates are currently increasing faster than data rates for Fibre Channel and similar disk-attachment technologies. iSCSI can thus address both the low-end and high-end markets with a single commodity-based technology. iSCSI preserves the basic SCSI paradigm, especially the command set, almost unchanged.

SCSI interface overview
Interface	Bus speed (MBytes/s)	Bus width (bits)	Max. cable length (meters)	Max. number of devices
SCSI	5	8	6	8
Fast SCSI	10	8	1.5-3	8
Wide SCSI	20	16	1.5-3	16
Ultra SCSI	20	8	1.5-3	5-8
Ultra Wide SCSI	40	16	1.5-3	5-8
Ultra2 SCSI	40	8	12	8
Ultra2 Wide SCSI	80	16	12	16
Ultra3 SCSI	160	16	12	16
Ultra-320 SCSI	320	16	12	16
iSCSI	limited only by IP network	N/A	N/A	??

External Links

SCSI Specs - http://www.t10.org/

The following table is compiled from various sources, across various languages. When English abbreviations or acronyms come from a non-English source, this is noted.
Entry	Source	Expression	Field
SCSI	English	Small computer systems interface	Computing
SCAM	English	SCSI Configured AutoMatically	Computer - (SCSI)
Source: compiled by the editor, based on several corpora (additional references).

Synonym: SCSI

Synonym: small computer system interface (n). (additional references)

Domain	Title
Books	SCSI Bench Reference (ENDL SCSI Series) (reference) Seagate Refreshes Its 7,200rpm SCSI Product One More Time [DOWNLOAD: PDF] (reference) The Programmer's Guide to Scsi (reference) (more book examples)

High Tech	EVO W6000MT P4-2.4GHZ 36GB SCSI (reference) (more camera examples; more video game examples; more computer examples; more electronic examples; more software examples)
Source: compiled by the editor from various references; see credits.

Subject	Topic	Quote
Business		This product offers a variety of interfaces, including USB, PCMCIA, IDE, SCSI, and PPT. The main products being marketed in Korea by Imation Korea include "2X Superdisk 120MB" drives, which are incorporated by many PC makers into their PCs. The "2X Superdisk 120MB" drive is a large-capacity FDD of an USB interface type, with an automatic error recovery function. (references)
Source: compiled by the editor from ICON Group International, Inc.; see credits.

"SCSI" is generally used as a noun (proper) -- approximately 84.71% of the time. "SCSI" is used about 85 times out of a sample of 100 million words spoken or written in English. Its rank is based on over 700,000 words used in the English language. Some parts-of-speech are not covered due to the samples used by the British National Corpus. (note: percents less than one-hundredth of one percent have been omitted)

Parts of Speech	Percent	Usage per 100 Million Words	Rank in English
Noun (proper)	84.71%	72	39,377
Adjective (general or positive)	11.76%	10	111,207
Noun (common)	2.35%	2	245,945
Noun (plural)	1.18%	1	339,140
Total	100.00%	85	N/A

Expressions using "SCSI": advanced SCSI Peripheral Interface ♦ fast SCSI ♦ scsi adaptor ♦ scsi controller ♦ scsi ID ♦ scsi initiator ♦ scsi interface ♦ scsi reconnect ♦ scsi target ♦ scsi voodoo ♦ wide SCSI. Additional references.
Hyphenated Usage
	Beginning with "SCSI": SCSI-1, SCSI-2, SCSI-3, scsi-based, scsi-ii, scsi-to-parallel.
	Ending with "SCSI": Ultra-SCSI.
Source: compiled by the editor from various references; see credits.

Language		Translations for "SCSI"; alternative meanings/domain in parentheses.
Korean		스카시. (various references)

Pig Latin		iscsay

Russian		инф) (borland, diskcopy, norton, readme, svga, symantec). (various references)
Source: compiled by the editor from various translation references.

Scrabble® Enable2K-Verified Anagrams
	Direct Anagrams: sics.
	Words within the letters "c-i-s-s"
	-1 letter: cis, sic, sis.
	-2 letters: is, si.
	Words containing the letters "c-i-s-s"
	+1 letter: cissy, cists, discs, fiscs, sices, sicks, spics.
	+2 letters: asdics, aspics, basics, cassia, cassis, ciscos, cistus, cosies, crasis, crises, crisis, crisps, crissa, cuisse, cuspis, cyesis, discos, discus, ecesis, musics, osmics, piscos, saices, schism, schist, scions, scries, scrims, scrips, sickos, slices, slicks, snicks, sonics, spicas, spices, spicks, stichs, sticks, stoics, viscus.
	+3 letters: abscise, ascaris, ascesis, ascites, bisects, bustics, caisson, camisas, camises, capsids, caseins, casings, casinos, casitas, cassias, cassino, casuist, cerises, cesiums, cessing, cession, cesspit, chaises, chassis, chiasms, chisels, chrisms, ciscoes, cissies, cissoid, civisms, classic, classis, colossi, consist, cosiest, cosigns, cosines, cosmism, cosmist, cousins, crissal, crissum, cruises, cubisms, cubists, cuirass, cuishes, cuisses, cuspids, cussing, cutises, dicasts, discase, discuss, dissect, ecdysis, ectasis, excises, fascias, fascism, fascist, fiascos, ficuses, fiscals, fossick, fustics, iceless, iciness, ictuses, incases, incests, incises, incross, incuses, insects, mastics, misacts, miscast, miscues, miscuts, mosaics, muscids, mycosis, mystics, oscines, ossicle, ossific, ovisacs, physics, prussic, psocids, racisms, racists, rustics, sacrist, scabies, schisms, schists, schizos, schriks, schtiks, schuits, scillas, scissor, scotias, scribes, scrimps, scripts, scrives, seasick, sebasic, seiches, seismic, septics, sferics, shicksa, shticks, sickees, sickens, sickest, sickies, sickish, sickles, silicas, silvics, sitcoms, slicers, sluices, socials, spastic, species, spicers, splices, statics, stricks, sycosis, syndics, tocsins, viscose, viscous.
	+4 letters: abscised, abscises, abscisin, abscissa, achiness, acidness, acidoses, acidosis, acrasias, acrasins, amnesics, aphasics, arcsines, arsenics, asbestic, ascarids, ascetics, ascribes, astricts, auspices, bicepses, biscuits, brassica, caddises, caesiums, caginess, caissons, cambisms, cambists, camisias, capiases, capsizes, casefies, cashiers, cassinos, cassises, casteism, castings, casuists, caustics, cellists, celosias, centesis, cercises, cessions, cesspits, cestoids, chamises, chamisos, charisms, chasings, chastise, chemises, chemisms, chemists, chiasmas, chiasmus, chiauses, chicness, chinless, chintses, chrisoms, chutists, chymists, cineasts, circuses, cissoids, cisterns, cistrons, cistuses, citruses, cladists, classico, classics, classier, classify, classily, classing, classism, classist, clastics, clevises, clonisms, closings, coassist, coesites, coexists, cognises, coituses, conioses, coniosis, consigns, consists, copyists, corsairs, cosiness, cosmisms, cosmists, coulises, coulisse, cowskins, cowslips, coziness, crimsons, crispens, crispers, crispest, crosiers, crossing, crosstie, cruisers, cuisines, cullises, cultisms, cultists, cursives, curtsies, cushiest, cushions, cuspides, cyanosis, cycasins, cyclists, cyclosis, cysteins, cystines, cystitis, cystoids, czarisms, czarists, dehisces, descries, dioceses, discants, discards, discased, discases, discepts, discerns, disclose, discoids, discords, discuses, disjects, dissects, distichs, ecesises, echoisms, eclipses, eclipsis, ekistics, elastics, episcias, eristics, escapism, escapist, exscinds, fascines, fascisms, fascists, fiascoes, fossicks, fuchsias, fuchsins, glacises, gneissic, gnostics, hibiscus, hospices, ickiness, incenses, incisors, inclasps, incloses, incrusts, inscapes, insculps, inspects, isochors, isopachs, isotachs, issuance, justices, kinesics, kirsches, kitsches, laciness, laicises, laicisms, licenses, locoisms, luscious, massicot, meniscus, miscalls, miscasts, miscites, misclass, miscodes, miscoins, miscooks, misfocus, miskicks, misspace, musicals, narcisms, narcissi, narcists, narcosis, necrosis, niceness, oculists, orchises, ossicles, pachisis, piscinas, plastics, pocosins, potassic, precises, princess, psychics, pycnosis, rachises, raciness, rescinds, richness, rickshas, rictuses, sackings, sacrings, sacrists, sacristy, sadistic, salicins, sanicles, sapphics, sarcoids, sauciest, scabiosa, scabious, scaliest, scampies, scampish, scandias, scansion, scanties, scariest, scariose, scarious, sceptics, schticks, sciatics, sciences, sciolism, sciolist, scirrhus, scissile, scission, scissors, scissure, sciurids, scolices, scotties, scraichs, scraighs, scrapies, scribers, scrieves, sculpins, scurries, scurvies, sections, senecios, sericins, services, seviches, shickers, shicksas, sickbays, sickbeds, sicklies, sickness, sickouts, sidecars, silences, silicles, silicons, siroccos, skeptics, slickers, slickest, slipcase, smirches, snickers, snitches, solecise, solecism, solecist, solicits, solstice, spaciest, spacings, spacious, spadices, spastics, specials, specious, spherics, spiciest, spicules, splicers, statices, stencils, stickers, stickles, stickums, stickups, stitches, stockish, stockist, stoicism, styptics, subcutis, subsonic, suckfish, suctions, suffices, suicides, suitcase, swastica, switches, systemic, systolic, tachisms, tachists, trisects, unsticks, vesicles, viceless, victress, viscoses.
Source: compiled by the editor from various references; see credits. SCRABBLE® is a registered trademark. All intellectual property rights in and to the game are owned in the U.S.A and Canada by Hasbro Inc., and throughout the rest of the world by J.W. Spear & Sons Limited of Maidenhead, Berkshire, England, a subsidiary of Mattel Inc. Mattel and Spear are not affiliated with Hasbro.