Small Computer System Interface
(SCSI) /skuh'zee/, /sek'si/ A
processor-independent standard for system-level interfacing
between a computer and intelligent devices including {hard
disks}, {floppy disks}, {CD-ROM}, {printers}, {scanners}, and
many more. SCSI-1 can connect up to seven devices to a single
{SCSI adaptor} (or "host adaptor") on the computer's bus.
SCSI transfers eight bits in parallel (it is an eight-bit bus,
but see {Wide SCSI}) and can operate in either {asynchronous}
or {synchronous} modes. The synchronous transfer rate is up
to 5MB/s. There must be at least one {target} and one
{initiator} on the SCSI {bus}.
SCSI connections normally use "{single ended}" drivers as
opposed to {differential drivers}. Single ended SCSI can
suport up to six metres of cable. Differential can support up
to 25 metres of cable.
A problem with SCSI is the large number of different
connectors allowed. Nowadays the trend is towards a 68-pin
{miniature D-type} or "high density" connector (HD68) for
{Wide 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 internal
wiring (Type 5, pin pitch 2.54 mm x 2.54 mm). {Apple
Computer} used a 25-pin connector on the {Macintosh} computer
but this connector causes problems with high-speed equipment.
SCSI was developed by {Shugart Associates}, which later became
{Seagate}. SCSI was originally called SASI for "Shugart
Associates System Interface" before it became a standard.
Original SCSI implementations were highly incompatible with
each other.
The original standard is now called "SCSI-1" to distinguish it
from {SCSI-2} and {SCSI-3} which include specifications of
{Wide SCSI} (a 16-bit bus) and {Fast SCSI} (10 MB/s transfer).
SCSI-1 has been standardised as {ANSI} X3.131-1986 and
{ISO}/{IEC} 9316.
{ASPI} is a standard {Microsoft Windows} interface to SCSI
devices.
{Usenet} newsgroup: {news:comp.periphs.scsi}.
{(news:comp.periphs.scsi)}
["System" or "Systems"?]
(1999-03-30)