SCSI adaptor

hardware (Or "host adaptor") A device that communicates

between a computer and its SCSI peripherals. The SCSI

adaptor is usually assigned SCSI ID 7. It is often a

separate card that is connected to the computer's bus

(e.g. PCI, ISA, PCMCIA) though increasinly, SCSI

adaptors are built in to the motherboard. Apart from being

cheaper, busses like PCI are too slow to keep up with the

newer SCSI standards like Ultra SCSI and Ultra-Wide SCSI.

There are several varieties of SCSI (and their connectors) and

an adaptor will not support them all.

The performance of SCSI devices is limited by the speed of the

SCSI adaptor and its connection to the computer. An adaptor

that plugs into a parallel port is unlikely to be as fast as

one incorporated into a motherboard. Fast adaptors use DMA

or bus mastering.

Some SCSI adaptors include a BIOS to allow PCs to boot

from a SCSI hard disk, if their own BIOS supports it.

Adaptec make the majority of SCSI chipsets and many of the

best-selling adaptors.

Note that it is not a "SCSI controller" - it does not control

the devices, and "SCSI interface" is redundant - the "I" of

"SCSI" stands for "interface".

(1999-11-24)