[Info-vax] Dave Cutler, Prism, DEC, Microsoft, etc.

[Rich Alderson]

koehler at eisner.nospam.encompasserve.org (Bob Koehler) writes:

> In article <mddskbqa0oi.fsf at panix5.panix.com>, Rich Alderson
> <news at alderson.users.panix.com> writes:

>> You're probably talking about the PDP-14 and PDP-16, and you're right, I
>> didn't count them as separate computer architectures.  I still don't.  If
>> instead you are counting the minimal variations among members of those
>> families as separate architectures, then we have a fundamental disagreement
>> on what that word means in this context, and have nothing substantial to
>> discuss.

>    I was aware that the word sizes were often common, but I'm under the
>    impression there were variations in the register sets and/or
>    instruction sets.  If those were minor, then I'd agree they were the 
>    same architecture.

The PDP-1 had a 12-bit address, 5 bits of opcode, and an indirect bit.  The
other 18-bit systems from DEC had a 13-bit address, 4 bits of opcode, and an
indirect bit; the opcodes were the same from the PDP-4 through the PDP-15.  The
differences were in additional IO devices and related conditions.  A PDP-15
would run PDP-4 code, but not vice versa.

An XKL Toad-1 will run PDP-6 user mode code, although the I/O instructions are
completely different.  The same is true of the KL10 and KS10 processors from
DEC:  User-mode PDP-6 code will run on them as well as on earlier PDP-10s.

PDP-5 code will usually run on a PDP-8, although there are a few places (like
the PC being memory 0000 on the -5) that may get you into trouble.

The table of differences between models of PDP-11 is three or four pages in the
processor manual, but no one says "Oh, that's not a PDP-11".

-- 
Rich Alderson                  "You get what anybody gets. You get a lifetime."
news at alderson.users.panix.com                           --Death, of the Endless