SCSI products include SCSI host adapters and controllers, SCSI converters, SCSI terminators, and SCSI switches.  Small Computer Systems Interface (SCSI) is an intelligent I/O parallel peripheral bus with a standard, device-independent protocol that allows many peripheral devices to be connected to the SCSI port. A single SCSI bus can drive up to eight devices or units: the host adapter or controller, and seven other devices. Each device is assigned a different SCSI ID, ranging from 0 to 7.  SCSI standards, product form factor, signalling type and level, terminator class, and terminator type are all important parameters to consider when searching for SCSI products.

Product Form Factor

The product form factor for SCSI products can be stand-alone unit, board-level units, ASIC, and rack mount.  Signaling type and level parameter to consider include single ended SCSI, multimode, and differential.  A SCSI terminator is an electrical circuit at the end of the SCSI cable designed for impedance matching.  With the terminator in place the electrical signals traversing the cable will not be reflected back when they reach the end of the cable.  It is important to remember that any SCSI segment in the system requires only two terminators and no more than two.  These two terminators must be placed at each end of the SCSI cable (not at devices at the middle of the bus).  All terminators require power to function. Normally this power is provided by the host adapter on the TERMPWR lines on the bus. Termination parameters to consider include terminator class and terminator type.  The termination class is either internal or external.  Choices for type include passive, active, active negation, high voltage differential, low voltage differential, multimode, forced perfect terminator, and high byte terminator.  Some devices have auto-termination support.  Other specifications to consider when searching for SCSI adapters and SCSI controllers include data transfer rate and data transfer mode.