SCSI ID is usually set with jumpers or switches and often labeled: ID0, ID1, ID2 ... and so on. They have binary values. For example, if the ID0 is turned ON, that's "1". Similarly if ID1 is ON, that's "2", and if ID2 is ON that's "4" and so on and so forth. By combining jumpers, any value from 0 to 7 can be set. For example, in order to get ID 5, you would jumper ID0 and ID2.
On the older devices the ID could be 0 to 7. The host adapter always had ID 7. Most PC operating systems preferred ID 0 as the boot drive.
However, wide devices now have ID's 0 to 15 but the host adapter still gets the 7 slot, and it's still easier to set the boot disk to 0.
In some high-end machines a SCSI backplane is available and where the disks plug in determines its ID.
How to Name The SCSI Disks:
All SCSI devices have slots (at the back of the drive) to plug in the power and the SCSI cable. Usually to the left of the cable you will see several small jumper blocks. To the far left you will notice SCSI ID and three jumper blocks. This is where you set up IDs 0 through 6.
