SCSI Extenders

SCSI extenders are stand-alone modules or cards used to extend the distance at which peripheral devices may be placed from the host computer. 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 extenders function by converting SCSI parallel signals into serial data, which is then transmitted to another extender that converts the information back to SCSI signals. The two extenders communicate in full duplex mode and provide transparent communications for the SCSI bus. They may be used in conjunction with any application where converting single-ended devices to LVD, or where longer cables on a single-ended SCSI interface are required. For example: RAID Systems and remote arrays, DLT & DAT Tape Drives, Jazz Drives (removable media), streaming tape drives, optical drives, laser printers, Hard disk drives, optical CD-ROM and CDR drives, optical juke boxes, etc.

There are two basics types of SCSI extenders: single-ended and differential. Single ended SCSI extenders carry each signal on only one wire. The other wire is grounded. Differential SCSI extenders transmit the voltage difference between two lines of the cable. There are two sub-categories of SCSI extenders: HVD (where 5 volts represent the SCSI signals), and LVD (which uses 3.3 volts to represent the SCSI signals).

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