UPGRADING REPAIRING PCs

118
Chapter 4—SCSI and IDE Hard Drives and Optical Drives
or 15, which is the highest priority ID. All other devices must have
unique IDs that do not conflict with one another. Some host
adapters boot only from a hard disk set to a specific ID. Older
Adaptec host adapters required the boot hard disk to be ID 0;
newer ones can boot from any ID. A SCSI device containing multiple
drives (such as a CD-ROM tower or changer) will have a single
ID, but each physical drive or logical drive will also be known by a
logical unit number (LUN). For example, a 5-CD changer is SCSI ID
#3. Each “virtual drive” or disc position within SCSI ID #3 has a
LUN of 0–4. So the last “drive” has drive letter J and is also identified
by Windows as SCSI ID#3, LUN 4.
Setting the SCSI ID
The methods for setting the SCSI ID vary with the device. For internal
drives, the settings are made with jumper blocks. Use Table 4.16
to set the jumpers. Note that the column to the left is the lowest
numbered ID jumper, which may be identified as A0 or SCSI ID0,
depending on the drive vendor.
Table 4.16 SCSI ID Jumper Settings
SCSI ID Jumper Settings
ID# A0 A1 A2 A3 (WD and Quantum Markings)
ID0 ID1 ID2 ID3 (Seagate Markings)
00 0 0 0 0
01 1 0 0 0
02 0 1 0 0
03 1 1 0 0
04 0 0 1 0
05 1 0 1 0
06 0 1 1 0
07 1 1 1 0
08 0 0 0 1
09 1 0 0 1
10 0 1 0 1
11 1 1 0 1
12 0 0 1 1
13 1 0 1 1
14 0 1 1 1
15 1 1 1 1
1 = Jumper On, 0 = Jumper Off