HP SureStore Optical Disk Drive User's Guide - C1114-90015

Appendix B B-5

Operating This Drive on a SCSI Bus

A Brief Overview of SCSI

Operating the Drive

on a SCSI Bus

The differential bus uses two lines for each signal and measures the voltage

difference between the two signals. Differential retains more signal quality than

single-ended and is not as sensitive to noise, allowing for a longer cable length. The

maximum allowable length of a differential bus is 25 meters (82 feet) for all types

buses (narrow, wide, fast, Fast-20).

Connectors

Narrow devices (50-pin) use the following connectors:

• 50-pin low-density clip Centronics-type (external)

This is a large connector that is similar to a printer cable. This type of connector

is gradually being replaced by the Micro D connector, described below.

• 50-pin high density Micro D (using thumbscrews or small clips) (external)

• This connector is similar to a D-type connector, but smaller and with smaller pin

holes placed closer together.

• 50-pin low-density ribbon (usually internal to the host)

Wide devices (68- pin) use the following connectors:

• 68-pin high density Micro D connector (external)

This connector is similar to a D-type connector, but longer and slimmer and with

smaller pin holes placed closer together. This connector is becoming the most

common.

• 68-pin high density ribbon (usually internal to the host)

NOTE For more complete information on the theory and operation of the SCSI bus, you

may want to go to:

Adaptec - major supplier in SCSI buses

www.adaptec.com

Symbios Logic - Working drafts of SCSI specifications