A SCSI host adapter is a device used to connect one or more other

SCSI Small Computer System Interface (SCSI, ) is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, electrical, optical and logical interface ...

devices to a

computer bus In computer architecture, a bus (shortened form of the Latin '' omnibus'', and historically also called data highway or databus) is a communication system that transfers data between components inside a computer, or between computers. This ex ...

. 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 A hard disk drive (HDD), hard disk, hard drive, or fixed disk is an electro-mechanical data storage device that stores and retrieves digital data using magnetic storage with one or more rigid rapidly rotating platters coated with magnet ...

CD-ROM A CD-ROM (, compact disc read-only memory) is a type of read-only memory consisting of a pre-pressed optical compact disc that contains data. Computers can read—but not write or erase—CD-ROMs. Some CDs, called enhanced CDs, hold both comput ...

) 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 PCI may refer to: Business and economics * Payment card industry, businesses associated with debit, credit, and other payment cards ** Payment Card Industry Data Security Standard, a set of security requirements for credit card processors * Pro ...

cards, either 32-bit or 64-bit. Older ones were based on the 16-bit

ISA Isa or ISA may refer to: Places * Isa, Amur Oblast, Russia * Isa, Kagoshima, Japan * Isa, Nigeria * Isa District, Kagoshima, former district in Japan * Isa Town, middle class town located in Bahrain * Mount Isa, Queensland, Australia * Mount Is ...

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.

Types

SCSI host adapters traditionally fall into two broad classes: * Simple, relatively low-performance cards that provide an inexpensive way to connect SCSI devices that do not demand a great deal of bandwidth: notably

drives and SCSI scanners. The cost varies but is typically in the order of $US40 or so. These were very common up until about 2000, but are now fairly rare: the demise of the ISA slot added a little to the cost; the great improvement in IDE technology (particularly in the case of

drives and

CD recorder In computing, an optical disc drive is a disc drive that uses laser light or electromagnetic waves within or near the visible light spectrum as part of the process of reading or writing data to or from optical discs. Some drives can only r ...

s) removed one major use, and the advent of USB made the expense of a SCSI interface unnecessary for most scanners. * High-end cards designed for maximum performance, usually for very high-speed hard drives, and especially for situations that require several high-speed drives (notably

server Server may refer to: Computing *Server (computing), a computer program or a device that provides functionality for other programs or devices, called clients Role * Waiting staff, those who work at a restaurant or a bar attending customers and su ...

s). These are almost always quite expensive, around $US200 or more. The advent of

serial ATA SATA (Serial AT Attachment) is a computer bus interface that connects host bus adapters to mass storage devices such as hard disk drives, optical drives, and solid-state drives. Serial ATA succeeded the earlier Parallel ATA (PATA) standard t ...

is expected to reduce the usage of high-end SCSI host adapters, but there is no current expectation that they will disappear in the near future.

Manufacturers

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. {{DEFAULTSORT:Scsi Host Adapter SCSI de:SCSI-Hostadapter