Personal Computer User's Guide

10-16
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External SCSI devices connected to the integrated Adaptec 7880 Ultra/Wide control-
ler through the 68-pin Ultra/Wide SCSI connector on the system back panel must
have a unique SCSI ID number from 0 to15. This SCSI ID number cannot conflict with
any SCSI ID number already assigned to a SCSI device connected to the 50-pin inter-
nal SCSI connector on the system board.
When SCSI devices are shipped from Dell, the default SCSI ID numbers for the pri-
mary and secondary controllers are assigned as follows:
 Primary SCSI controller:
— The primary 7890 Ultra2/Wide LVD SCSI controller is configured through the
computer’s basic input/output system (BIOS) as SCSI ID 7.
— The first internal SCSI hard-disk drive is configured as SCSI ID 0. (The drive
used to boot your system should always be configured as SCSI ID 0.)
 Secondary SCSI controller:
— The secondary 7880 Ultra/Wide SCSI controller is configured through the
computer’s BIOS as SCSI ID 7.
— A SCSI CD-ROM drive is configured as SCSI ID 5.
— A SCSI tape drive or digital audio tape (DAT) drive (if installed) is configured
as SCSI ID 6.
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 devices installed by Dell are configured correctly during the manufacturing pro-
cess. You do not need to set the SCSI ID for these SCSI devices.
If you attach additional optional SCSI devices, refer to the documentation that came
with each device for information about setting the appropriate SCSI ID number.
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SCSI logic requires that termination be enabled for the two devices at opposite ends
of the SCSI chain and disabled for all devices in between. However, because both
SCSI controllers are self-terminating and because all internal SCSI cables provided by
Dell have active termination at the end of the cables, any SCSI devices you install
should have termination disabled on the devices.
Furthermore, when attaching external SCSI devices, you should use only external
SCSI cables with active termination on the cable. When used with this type of cable,
all external SCSI devices also need to have termination disabled on the devices.
See the documentation provided with any optional SCSI device you purchase for infor-
mation on disabling termination on the device.
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