I'd have to go dig up my docs and look at the actual pin assignments
to be 100% sure of exactly what's where, but the general concept that
P1 is primarily VME, P2 is primarily Sun's private bus, and P3 is primarily
VME again, mostly power, is valid.

   Whether two machines could coexist in a chassis is an interesting
question. In theory, if on different P2 segments, each would have a
private memory bus. The VME bus to devices would be shared, but many
CPU boards can be jumpered for VME slave mode. By clever trimming of
the kernels, you could keep them from trying to grab the same devices.
I guess it would hinge on whether "slave mode" is purely a hardware-level
thing, invisible to the OS, or requires that the OS make or not make
certain assumptions. Electrically speaking, I think it would work, but
whether it would require OS modification or not is an open question.
   I've heard rumors of clustering experiments using CPU boards with
onboard memory, speaking TCP/IP to each other across the VME bus, but
that was using very custom software.

   --James B.