On 05/11/2019 06:14 PM, Warren Toomey via cctalk wrote:
I'm building my own 8-bit CPU from TTL chips, and this caused me to think:
how were 32-bit minis built in the late 70s and early 80s? In particular,
how was the ALU built? I know about the 74181 4-bit ALU, and I know (from
reading A Soul of a New Machine) that PALs were also used.
Did companies get custom chips fabricated, or was it all off-the-shelf chips
with a few PALs sprinkled in?
There were also the AMD2901, 2903, 29203 family of bit-slice
components, with the 2910 sequencer. I built a 32-bit basic
microengine in about 1982, but the software development
effort eventually led me to stop work on it. I was planning
to implement the IBM 360 instruction set, with extensions,
as it was very easy to implement with microcode.
See http://pico-systems.com/stories/1982.html for some
description and photos.
Apollo built some machines which I think were programmed at
the microinstruction level, without microcode, using 2903's,
I think.
The VAX 11/780 used 74S181 ALU chips, I think. There were
not all that many 32-bit minis.
I can think of Interdata 7/32 and 8/32 models that were
32-bit. SEL also made a 32-bit mini.
The VAX 11/780 was completely done with off-the-shelf ICs.
Later VAXes went to semi-custom ICs, and the MicroVAX line
used full-custom ICs. I suspect many other makers were so
small, they could only use off the shelf parts.
Jon
