[Simh] PDP-15/76

[Bob Supnik]

I've pulled together the hardware pieces for the PDP-15/76 (PDP-15 with 
UC15 PDP-11 IO processor), so now it's time to consider what software 
can be run.

The most likely candidate is XVM/DOS-15. While vanilla DOS-15 had UC15 
support at some point, neither a complete source kit nor the appropriate 
restore DECtape images seem to be available. The XVM/DOS-15 kit has all 
required DECtapes, but it lacks the paper-tape elements. Fortunately, 
these exist in source form in the XVM/DOS-15 source kit.

ABSL11 - a PDP-15 read-in mode tape that allows PDP-11 absolute binary 
tapes to be read into shared memory and moved to private memory. (This 
is not strictly necessary, because the PDP-11 side has its "hardware" 
binary loader via the LOAD command.) This is used to load PIREX. It must 
be assembled on the PDP-15.

PIREX - a PDP-11 absolute mode tape that runs the PDP-11 IO executive. 
It has to be assembled on an -11, so the source must be loaded into an 
RT11 system, assembled, and punched out as a binary paper tape image. 
It's possible that the macro11 cross assembler could be used instead.

DOSSAV - a PDP-15 binary tape that restores a distribution kit (usually 
two DECtapes) to RF, RP, or RK disk. It must be assembled on the PDP-15. 
It uses PIREX.

RKBOOT - a PDP-15 read-in mode tape that uses PIREX to boot a PDP-15 
operating system off the RK15 (an 18b RK11). It must be assembled on the 
PDP-15. It uses PIREX.

/Bob