[G4] SCSI ID question

[Alex]

On Tuesday, Mar 2, 2004, at 00:49 Canada/Eastern, Donald Town Jr. wrote:

> I just picked up a G3 a few days ago [...]

Which one? We should focus on specifics.

> After popping two of the newer drives in and starting up, (Thinking I 
> had
> successfully changed a scsi id) [...]
> Also, the profiler said one drive was on ata 1 and the other on ata 0.
> Both had ID 0 [...].

There seems to be some confusion here, both in the original post and in 
some of the replies.

SCSI and ATA buses are different and separate, so don't confuse them. 
We don't know which G3 you're working with, so we can only talk in 
generalities. Keep in mind that a "bus" is a data pipe, a highway on 
which data travels from one place to another. SCSI and ATA are 
different types of buses. If you're keen on trivia, ATA stands for 
"Advanced Technology Attachment", and was originally called IDE 
(Integrated Drive Electronics); SCSI stands for "Small Computer System 
Interface". The former was initiated by Compaq, the latter by what 
later became Seagate.

To begin with, floppy drives should be kept out -- as a rule, they're 
attached to neither of these two bus types.

In general terms (and greatly simplifying), a computer will usually 
have two ATA buses, one straight ATA (to which hard drives are 
attached) and one ATAPI (i.e., packet-interface, to which removable 
drives, such as CDs and Zips, are attached). Each bus can take two 
drives, a master (ID 0) and a slave (ID 1). (These names are for 
convenience's sake, they do not imply any subordination.) On older 
machines, this ID has to be set in hardware at installation (usually 
with a jumper); newer machines have a facility called Cable Select, 
which allows the bus controller to set the ID by itself.

The computer may also have one or more SCSI buses, either on the 
motherboard or on expansion cards. The SCSI bus is more versatile than 
the ATA bus, but more expensive. Each SCSI bus supports up to 7 
daisy-chained devices, each with a unique ID (or address) ranging from 
0 to 6. The ID 7 (i.e., 8th device) is normally reserved for the 
computer ("initiator"). Normally, the SCSI ID of a device is set in 
hardware (usually by means of one or more jumpers) at installation (for 
int'l devices) or by means of a switch before powering up (for ext'l 
devices). Both int'l and ext'l devices can be attached to the same SCSI 
bus. If two devices with the same ID are present on the bus, one or 
both of the devices will malfunction, and very likely also the entire 
bus. SCSI buses require to be correctly terminated; if they're not, 
they may malfunction. Each SCSI bus is independent of the other, and 
thus IDs and termination on one bus have no relevance to the other bus, 
except inasmuch as they affect the initiator (e.g., two devices with 
the same ID on one bus may cause the bus to malfunction, which may 
cause the computer to crash, which may lead to loss of data on the 
other SCSI bus.)

f