Just because we are on the subject already.
What is the last version of the firmware ?
I can't remember exactly, but the 100A was definitely 4.xx series (maybe
4.12?) while the 100B was definitely 5.xx series (maybe 5.03A). I've
never seen different values on any Rainbow, though, suggesting that the
boot roms were finalized before manufacturing started and never again
updated. Could be wrong, though.
Is the only difference between the -A and -B the firmware ROM? If you got
the later firmware and put it into a -A mainboard would the machine (a)
still work and (b) let you boot from a hard drive (asuming you'd also
fitted the controller card)?
-tony