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D
appendix
SCSI G
UIDELINES
This appendix contains helpful guidelines for installing Small Computer System
Interface (SCSI) devices.
Guidelines for Installing Optional
SCSI Devices
When installing and operating SCSI devices, you must adhere to the following
guidelines:
A single SCSI controller allows you to daisy-chain up to seven SCSI devices. These may be hard
drives, CD-ROM drives, scanners, tape drives, and/or other SCSI devices installed in your
computer. Most SCSI controllers have connectors for both internal and external devices.
Every SCSI device must have a unique identification (ID) number. The SCSI controller
identifies signals to and from a SCSI device by its SCSI ID number rather than its location. Moving
a SCSI device from one position to another on the SCSI chain does not affect the communication
between the controller and the SCSI device. Check the information that came with your device for
the recommended SCSI ID number to be applied. The reserved and available SCSI ID numbers for
Compaq computers are as follows:
0 is reserved for the primary hard drive and has the lowest device priority.
1 through 6 are available for use by all SCSI devices.
7 is reserved for the system board and has the highest device priority.
Every SCSI chain or circuit must be terminated (closed) at both ends. Termination can be
accomplished in one of several ways:
Use a cable with a built-in terminator.
Use a cable with a terminating resistor plug in the last connector.
Connect a SCSI device, with the termination enabled, into the last connector.
Some systems have both ends of the SCSI cable connected to, and terminated by,
the system board.
Turn on all external SCSI devices before turning on power to the computer. This enables the
controller to recognize the external SCSI devices and automatically reset. When an external SCSI
device is connected to the external SCSI connector on the rear panel of the computer, that device
becomes the end of the SCSI chain and must be terminated.
All SCSI hard drives must be either internal or external, but never both. The system does
accommodate a combination of other internal and external SCSI devices, such as SCSI tape and
CD-ROM drives.
Compaq Deskpro 4000 and 6000 Series of Personal Computers
D-1
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