TECH BASICS

SCSI - SCSI stands for Small Computer System Interface.

The normal internal cable for SCSI is a 50 conductor ribbon, with all odd numbered conductors grounded. Two conductors, numbers 25 & 26, are often left not-connected, as they deal with Terminator power, and can be easily shorted by cable reversals. There are no twists in this cable, and it's length may be a maximum of 6 meters. But one is advised to use minimum lengths to improve timing. Up to seven drives, or devices may be attached to an SCSI cable. Each is daisy-chained on the cable, or, when a device has two connectors, another cable may be "spliced" into the chain starting at the second connector, and continued on. Care must be taken to insure that cables and connectors are not reversed, as this would short pin 26 (TERMPWR) to ground, and likely damage the drive or controller. Also, as explained earlier, the terminating resistors should remain only on the controller (Host Adapter) and the LAST drive on the cable, regardless of it's address. The Differential SCSI requires balanced lines, and is used mostly on high-end workstations.