First of all thanks for reading this - you are very brave.

I have used a Calluna 520 MB PCMCIA hard drive in a fleet of custom PC's
for years. They have worked well overall. However, this drive has
ceased production and has been replaced by another model. It's branding
is identical, but the model number has changed from ct520rm to ct521rm.
This apparently small change has caused me a ton of problems.

I should mention that the target OS on these puppies is SCO Unix. For
legacy sake I cannot upgrade this.

To make a long story somewhat shorter, all of my loading methods for
these drives are now invalid. I cannot load this ct521rm drive like I
used to be able to. The Unix load process works fine, but the drives
will not boot reliably. BIOS sees the drives identically - the same
parameters (c/h/s). I cannot ghost a ct520rm to a ct521rm drive either.
As before, the ghost operation works flawlessly (this is using raw
sector by sector process as it is Unix) but booting the drive proves to
not work. The drive does begin to boot, but dies shortly after.

I don't know much about hard drive characteristics and internal
workings, but because the drive begins to boot I would assume the mbr is
working properly. After this stage, I am not sure.

What could be so different about these ct521rm drives? Does anybody
have experience with them or similar problems with other models?

As a last ditched effort ... is there anyway to fool this drive into
behaving like a ct520rm? I mean, in BIOS when it is identified - can I
get overwrite the drive somehow to act and report as a ct520rm? I know
this will fail if there are actual hardware level differences - but I am
willing to potentially induce a few casualties to find out...

Thanks for your time.