I have two HDs, call them A & B. Linux (RH7.2) is installed on both and
both are bootable.

1. If I put A as the Primary on IDE1 and B as the Primary on IDE2, then I
can boot to A and mount B's partitions as /dev/hdcx (where x is the
appropriate number). And using RH's hardware browser, I can look at the
partitioning on both of them.

2. THEN If I put B as the Primary on IDE1 and A as the Primary on IDE2,
then I can boot to B
BUT I can't mount any partition of A. ( "... is not a valid block
device" ).
AND I can't start the hardware browser -- it claims that it can't open
/dev/hdc which is where A is located.

BUT the BIOS sees both drives and during bootup they are both
enumerated!

3.. Even more confusingly, if I put B as the Primary on IDE1 (as #2 above)
and put A as the Secondary on the same IDE channel then I can boot B and
mount A the same way I did for the reverse situation.

MY QUESTION:
Is this a Linux problem or a BIOS/hardware problem?

For the record, A is a Maxtor 40GB drive and B is an 80 GB drive.

All suggestions, hints, and solutions are gladly welcome.

TIA
Norm