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.
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“The Landlord is a gentleman ... who does not earn his wealth. He has a host of agents and clerks that receive for him. He does not even take the trouble to spend his wealth. He has a host of people around him to do the actual spending. He never sees it until he comes to enjoy it. His sole function, his chief pride, is the stately consumption of wealth produced by others.”
—David Lloyd George (18631945)