The Free On-line Dictionary of Computing (30 December 2018):
(Or "host adaptor") A device that communicates
between a computer and its SCSIperipherals. 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
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".