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20 ST11950 and ST12550 Installation Guide, Rev. D
Setting the SCSI ID jumpers
Each device on the SCSI chain must have a unique SCSI
ID. The host system’s SCSI controller usually uses the
highest-numbered ID available (ID7 in non-wide sys-
tems); therefore the lower-numbered SCSI IDs are nor-
mally used for the other SCSI devices such as this
Barracuda disc drive.
Note. Most SCSI controllers (host adapters) allow you to
skip a SCSI ID. For example, you can have ID0,
ID1, and ID3 (skipping ID2). Other controllers do
not allow this so be sure to refer to your system or
controller user’s manual for details about its re-
quirements for proper SCSI device installation.
Use connector J4 to set the SCSI ID on ST11950N/ND
and ST12550N/ND drives (Figure 3). Use connector J5
to set the SCSI ID on ST11950W/WD and ST12550W/WD
drives (Figure 4). Most Barracuda 1 and 2 disc drives are
factory set with the SCSI ID set at 0. To change the SCSI
ID, install jumpers on the appropriate pins as shown in
the illustrations.
If, after completing the installation process, the drive’s
LED does not show on/off activity when the host is trying
to communicate with the drive, a duplicate SCSI ID may
be the problem. If this is the case, change the ID so that
each device on the SCSI chain has its own unique ID.