I need help with SCSI IDs...

[Antoneo]

Just need someone(s) verification or answer to following...
SCSI 1 has 7 possible IDs, correct? and they range from 0 - 6?
SCSI 2 has 16 possible IDs and they range from 0 to 15?

Help! im confused!

 

[Antoneo]

there's gotta be a scsi guru lurking somewhere ^^^

 

[Ben]

Your partially correct but the cutoff point is not between the SCSI 1 and the SCSI 2 group. It's somewhere mixed in the SCSI 2 group with the wide devices having 16 ID numbers and the narrow devices having only 7.

If you browse around here at SCSI school you should find your answers.

 

[mastertech01]

Wide devices should be reserved for ID 8 and up as the wide buss is given priority during wide negotiation on those ID. That is primarily the reason CDROMS and such that run at Ultra or lower speeds should be run on IDs below 7 with 7 reserved for the device. And of course if you boot from SCSI that is usually reserved for ID 0 or 1 but on some card can be any drive up to ID 15. Some controllers support 30 devices..

 

[DoctorBooze]

It's not SCSI-1 or SCSI-2, it's narrow and wide. Narrow IDs run 0-7, wide IDs run 0-15. Usually the host adapter (SCSI card) will be ID 7. If you're mixing narrow (e.g. CD ROM, tape) and wide (e.g. hard drive) drives on one SCSI chain, you need to set all the narrow devices to have IDs 0-6. Wide devices can use IDs 0-6 as well, but if you use IDs 8-15, the host adapter will know already that they're wide, and won't have to ask them (not that it matters if it does have to).

It used to be that you had to have your boot drive on ID 0, and while nowadays most host adapters will let you have your boot drive on any ID, it still seems to sort some problems out to stick with using ID 0.

Controllers supporting 30 devices have two separate wide SCSI channels which operate independently. Controllers supporting 45 devices have three channels.

Incidentally, SCSI-1 and SCSI-2 are essentially the protocols used over the bus (SCSI-3 is the most recent version), though the standards do make references to which physical standards are acceptable. Narrow, wide, fast, ultra, ultra-2, ultra-3, single-ended, high-voltage differential, low-voltage differential and fibre channel are all variations on the physical standards involved.