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PDI-00440-70, Rev. A01

INTRODUCTION

This document describes the installation procedures for a 68-pin Wide SCSI bus cable (PDB-00440-7x)

in the following four types of chassis:

•

Deskside

•

AM-990 and AM-990 double-wide (jumbo): these chassis accept either a standard Wide SCSI

cable or the High-Capacity Wide SCSI Internal Cable, PDB-00440-75. This cable allows up to

nine internal devices, but no external cabling.

•

Pedestal

•

Rack mount

After general discussions of the Wide SCSI bus, device compatibility, and electronic handling

precautions, we give general installation guidelines and specific procedures for each chassis.

About the Wide SCSI Bus

The Wide SCSI bus is twice as wide as the “narrow” SCSI bus: two bytes, or 16 bits plus 2 parity bits.

Doubling the width of the data path doubles the maximum transfer rate to 20MB per second. The Wide

SCSI bus has the following advantages:

•

Disk-intensive applications are potentially faster with Wide SCSI disk drives.

•

It supports up to 15 devices, where standard SCSI supports only seven, so you can potentially

work with bigger configurations.

On Alpha Micro computers which support both narrow and Wide SCSI busses, you can use only

one of the two busses at a time. You cannot install both narrow and Wide SCSI cables and use

devices attached to both.

To ensure reliable SCSI operation, the SCSI bus must be

actively

terminated. The passive

external terminators used on earlier AMOS systems are not adequate. Your upgrade kit includes

an active terminator for the wide bus (PRA-00222-20).

Please note that, even though the names may suggest differently, the Wide SCSI cable and

connector are physically narrower than their “narrow” SCSI counterparts.

COMPATIBILITY

You can attach both narrow and Wide SCSI-2 devices to the Wide SCSI bus. To attach narrow devices to

the Wide SCSI bus, you need an adapter (PDB-00440-91) for each device. The adapter allows the 68-

conductor bus cable to mate with the 50-pin connector on the SCSI-2 device and terminates the unused

signal lines on the SCSI-2 device.

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Alpha Microsystems AM-647 Bedienerhandbuch Seite 4