Dell OptiPlex Gxi - Manual (Page 89)

Installing Drives 7-11
SCSI ID Numbers
Each device attached to a SCSI host adapter card, as well
as the card itself, must have a unique SCSI identification
(SCSI ID) number from 0 to 7. When SCSI devices are
shipped from Dell, the default SCSI ID numbers are
assigned as follows:
• A SCSI host adapter card is configured as SCSI ID 7.
• A SCSI tape drive or digital audio tape (DAT) drive
is configured as SCSI ID 6.
• A SCSI CD-ROM drive is configured as SCSI ID 5.
• SCSI hard-disk drives are usually configured as
SCSI ID 0. (The drive used to boot your system
should always be configured as SCSI ID 0.)
NOTE: There is no requirement that SCSI ID numbers be
assigned sequentially or that devices be attached to the
cable in order by ID number.
SCSI Cable and SCSI Termination
The type of cabling you receive with your SCSI device
depends on the type of device you are installing.
• If you are installing an internal narrow SCSI device
(such as a CD-ROM drive or tape drive), you have a
50-pin internal SCSI cable as shown in Figure 7-14.
One end of this cable attaches to the SCSI host
adapter. The three connectors on the other end of the
cable are used for attaching up to three narrow SCSI
devices installed in the externally accessible drive
bays.
Figure 7-14. Internal SCSI Cable
• If you are installing an internal wide SCSI device
(such as a wide SCSI hard-disk drive), you have a
68-pin internal SCSI cable as shown in Figure 7-14.
One end of this cable attaches to the SCSI host
adapter and the two connectors on the other end of
the cable are used for attaching up to two SCSI hard-
disk drives installed in the hard-disk drive bracket.
• If you are installing an external SCSI device, you
have a shielded external cable that connects to the
external SCSI connector on the SCSI host adapter
card. You have a separate power cable to connect the
SCSI device to an alternating current (AC) power
source.
Before installing SCSI devices in your computer, you
must configure the termination on your SCSI device(s) to
conform to the guidelines shown in Table 7-1. In
Table 7-1, the term “last device” refers to the device
attached to the end connector on the corresponding SCSI
cable. For instructions on enabling and disabling termina-
tion, see the documentation for your SCSI host adapter
card.
68-pin SCSI cable
(to hard-disk drive)
50-pin SCSI cable
(to device in externally
accessible drive bay)
CAUTION: Do not connect devices to all three con-
nectors (internal narrow connector, internal wide
connector, and external connector) on a single SCSI
host adapter card. Such a configuration is a viola-
tion of the SCSI specification. You can safely
connect devices to any two of these three connectors
on a single SCSI host adapter card.