What is a SCSI ID number?

Answer 1

SCSI - Small Computer System InterfaceSCSI is an industry standard system interface, which allows multiple peripheral devices to be installed on the system. The number of devices that can be installed depends on the type of SCSI Host adapter that you have installed in your system. Most SCSI systems have an older "Narrow" 8-bit SCSI host adapter, which have 8-bit data paths and allow for up to 7 devices to be installed on the same channel. Newer "Wide" Host adapters have 16-bit wide data paths and provide support for up to 15 devices.

A SCSI ID is a unique identifier assigned to each SCSI device on the bus. It determines the SCSI device's priority. There are 16 IDs, ranging from 0 to 15. The order of the priorities is a bit unusual. From highest priority to lowest they are: 7, 6, 5, 4, 3, 2, 1, 0, 15, 14, 13, 12 ,11, 10, 9, 8. ID 7 is almost always reserved for the SCSI Host Adapter. The other IDs are free to be assigned as desired, although your computer may have assigned them automatically.

Never assign the same ID to more than one device.

Answer 2

A standard SCSI controller can handle up to 7 devices per channel. Each device on this channel must be given a SCSI ID number (1 through 7 in this case) to avoid conflicting with the other devices. This is usually done with jumpers, but may also be done with toggle switches, or even through software.