Re: Why VAX Was the Ultimate CISC and Not RISC

Anton Ertl <anton@mips.complang.tuwien.ac.at> schrieb:

Thomas Koenig <tkoenig@netcologne.de> writes:

Anton Ertl <anton@mips.complang.tuwien.ac.at> schrieb:
>

Have TTL chips advanced between the VAX and the first HP-PA
implementation?  I don't think so.

>
Oh yes, they did; there were nine years between the launch of the
VAX and the launch of HP-PA.

>
So what?
>

and you can see pictures
at https://computermuseum.informatik.uni-stuttgart.de/dev_en/hp9000_840/

>
Nice!  The pictures are pretty good.  I can read the markings on the
chip.  The first chip I looked at was marked 74AS181.  TI introduced
the 74xx series of TTL chips starting in 1964, and when I read TTL, I
expected to see 74xx chips.  The 74181 was introduced in February
1970, and I expected it to be in the HP-PA CPU, as well as in the VAX
11/780.  <https://en.wikipedia.org/wiki/74181> confirms my expectation
for the VAX, and the photo confirms my expectation for the first HP-PA
CPU.
>
The AS family was only introduced in 1980, so there was some advances
between the VAX and this HP-PA CPU indeed.  However, as far as the
number of boards is concerned, a 74AS181 takes as much space as a
plain 74181, so that difference is irrelevant for that aspect.
>
I leave it to you to point out a chip on the HP-PA CPU that did not
have a same-sized variant avalable in, say, 1975.

What I found intruiging are the chips that have numbers on paper
on them, like 09740-81710.  That chip has a MMI logo still sticking
out.  This is the logo of Monolithic Memories, Inc. which developed
the PAL chips of "Soul of a New Machine" and Eclipse MV 8000 fame.
At https://en.wikipedia.org/wiki/Programmable_Array_Logic you can
see the logo of the company.

PALs were not available for the VAX development, and they certainly
made implemting logic far less cumbersome, and they took up far less
space than their equivalent in logic gates (again, as described in
"The Soul of a New Machine", where Tom West gambled the development
on MMI getting its act togetther).

Given a (very rough) estimate that each PAL replaced four standard
logic chips of simlar size, my guess would be that it saved
them toe equivalent of two to three circuit boards, not bad.

Another striking thing is how densely the circuit boards are packed,
compared to the VAX boards one finds.  I suspect they had access
to more layers of printed circuit board than DEC ten years earlier.