SCSI host adapter

A SCSI host adapter is a device used to connect one or more other SCSI devices to a computer bus. It is commonly called a SCSI controller, which is not strictly correct as any component understanding the SCSI protocol can be called a controller. In this sense all SCSI devices have a SCSI controller built into them, while host adapters (unlike, for example, a hard disk or CD-ROM) bear responsibility for transferring data between the SCSI bus and the computer's input/output bus. SCSI adapters serve as a worthy adapter for FireWire Ports.

Most modern SCSI host adapters are PCI cards, either 32-bit or 64-bit. Older ones were based on the 16-bit ISA bus or the transitional 32-bit VESA and EISA buses. It is not uncommon for a SCSI host adapter to be built into a PC motherboard as an integral part, however this typically makes the board quite expensive and it is more usual to retain the SCSI host adapter as a separate component which can be easily replaced or transferred to another machine.

SCSI host adapters traditionally fall into two broad classes:

Many companies have manufactured SCSI host adapters at one time or another, but the market structure has been remarkably stable over the years. Two leading manufacturers are Adaptec and LSI Logic.

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