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71 Chapter 7
7.2 Understanding SCSI
SCSI (pronounced .scuzzy.) stands for Small Computer Systems Inter-
face. SCSI is an industry standard computer interface for connecting
SCSI devices to a common SCSI bus.
A SCSI bus is an electrical pathway that consists of a SCSI interface
installed in a computer and one or more SCSI devices. SCSI cables are
used to connect the devices to the SCSI interface. For the SCSI bus to
function properly, a unique SCSI ID must be assigned to the SCSI inter-
face and each SCSI device connected to it, and the SCSI bus must be
properly terminated.
7.3 SCSI IDs
Each device attached to the SCSI bus, as well as the SCSI controller
itself, must be assigned a unique SCSI ID number from 0 to 15. A SCSI
ID uniquely identifies each SCSI device on the SCSI bus and determines
priority when two or more devices are trying to use the SCSI bus at the
same time.
Refer o the device.s documentation to set the SCSI ID. Here are some
general guidelines for SCSI IDs:
• For internal SCSI devices, the SCSI ID usually is set by configuring a
jumper on the device.
• For external SCSI devices, the SCSI ID usually is set with a switch on
the back of the device.
• SCSI ID numbers don.t have to sequential, as long as the SCSI control-
ler and each device has a different number.
• For example, you can have an internal SCSI device with ID 0, and an
external SCSI device with ID 6.
• SCSI ID 7 has the highest priority on the SCSI bus. The priority of the
remaining IDs, in descending order, is 6 to 0, then 15 to 8.
• The on-boards SCSI interface is preset to SCSI ID 7 and should not be
changed. This gives it the highest priority on the SCSI bus.
• Most internal SCSI hard disk drives come from the factory pre-set to
SCSI ID 0.
• If you have 8-bit (or Narrow) SCSI devices, they must use SCSI IDs 0,
1, 2, 3, 4, 5, or 6. SCSI ID 0 is recommended for the first SCSI hard
disk drive.