> > ... or could you? Didn't PDP8 come in all three versions?
>
> Yes it did, but there were _slight_ differences in the instruction set
> IIRC (rather like the differences in the PDP11 instruction set between
> similar-ish models).
The instructionset differences largely are in the OPR group where some of
the microcoded undocumented combinations were actually useful. When
viewed from the older members twoward the newest this is not a great
problem. the extended arithmetic however there were many flavors
that were somewhat compatable.
> But having a straight-8, a PDP8/e and a DECmate all running side by side
> would be an interesting exhibit. Pity I can't do it...
a PDP-5, straight-8, 8I, 8E, 8A and DECMATE (I/II/III?). Each represents
a level of difference on the base design. For example the 8A had
mechanism in hardware for stacks (actually IOTS so it's retrofitable!).
The DECmates represent two different chips the 6100 (base 8Eish) and the
6120 (more 8Aish) both having a control pannel mode unique to them.
The commonality is great from the 5 though the DMIII that you can wite
program that run on both. This made the PDP-8 series likable (software
investment).
Allison
Received on Fri Oct 22 1999 - 14:25:25 BST
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