Small Computer System Interface

small computer system interface

[¦smȯl kəm¦pyüd·ər ‚sis·təm ′in·tər‚fās] (computer science) An interface standard or format for personal computers that allows the connection of up to seven peripheral devices. Abbreviated SCSI (scuzzy).

Small Computer System Interface

(hardware, standard)(SCSI) /skuh'zee/, /sek'si/ The mostpopular processor-independent standard, via a parallel bus,for system-level interfacing between a computer andintelligent devices including hard disks, floppy disks,CD-ROM, printers, scanners, and many more.

SCSI can connect multiple devices to a single SCSI adaptor(or "host adaptor") on the computer's bus. SCSI transfers bitsin parallel and can operate in either asynchronous orsynchronous modes. The synchronous transfer rate is up to5MB/s. There must be at least one target and oneinitiator on the SCSI bus.

SCSI connections normally use "single ended" drivers asopposed to differential drivers. Single ended SCSI cansuport up to six metres of cable. Differential ended SCSI cansupport up to 25 metres of cable.

SCSI was developed by Shugart Associates, which later becameSeagate. SCSI was originally called SASI for "ShugartAssociates System Interface" before it became a standard.

Due to SCSI's inherent protocol flexibility, large supportinfrastructure, continued speed increases and the acceptanceof SCSI Expanders in applications it is expected to hold itsmarket.

The original standard is now called "SCSI-1" to distinguish itfrom SCSI-2 and SCSI-3 which include specifications ofWide SCSI (a 16-bit bus) and Fast SCSI (10 MB/s transfer).

SCSI-1 has been standardised as ANSI X3.131-1986 andISO/IEC 9316.

A problem with SCSI is the large number of differentconnectors allowed. Nowadays the trend is toward a 68-pinminiature D-type or "high density" connector (HD68) forWide SCSI and a 50-pin version of the same connector (HD50)for 8-bit SCSI (Type 1-4, pin pitch 1.27 mm x 2.45 mm).50-pin ribbon cable connectors are also popular for internalwiring (Type 5, pin pitch 2.54 mm x 2.54 mm). Apple Computer used a 25-pin connector on the Macintosh computerbut this connector causes problems with high-speed equipment.Original SCSI implementations were highly incompatible witheach other.

ASPI is a standard Microsoft Windows interface to SCSIdevices.

Usenet newsgroup: news:comp.periphs.scsi.

news:comp.periphs.scsi.SCSI Trade Association & FAQ http://scsita.org/.

small computer system interface

Small Computer System Interface