[Simh] Musings on potential SIMH candidate systems

[Alan Frisbie]

I am only just getting started with SIMH, so perhaps I'm getting
a bit ahead of myself, but here goes...

A classic graphics system of the early 1970s was the Imlac PDS-1.
The display was a vector-stroke type, driven by a display list in
memory and continuously refreshed.   It had a CPU for
communicating with a host (typically a PDP-10) and local
calculations, and a GPU (Graphics Processing Unit) for executing
the elements of the graphics display list, both running out of
the same memory.   Peripherals were generally limited to a serial
line, the light pen, and a single switch (often a foot switch).

The CPU looked very much like a 16-bit PDP-8, which should be
almost trivial to simulate.   The GPU would be a bit trickier,
as it would have to draw lines on the host's display.   The real
problem, as I see it, would be how to have *two* simulated
computers operating simultaneously from the same memory.   I seem
to recall a discussion on this list about how that would be
difficult, but can't recall the details.

Does anyone have any ideas on how this might be done?

I would be interested in doing it, as I just happen to have an
Imlac PDS-1D here, and would like have a simulator before I sell
the actual unit.   I also have a complete set of documentation
with all schematics, plus some software.


A second system of interest is the CDC 6600.   Again, the problem
as I see it is combination of a CPU and multiple PPUs (Peripheral
Processing Units).   It also used ones-complement arithmetic,
which might cause difficulties.   Does anyone have any thoughts
on these matters?

Alan Frisbie