How were 32-bit minis built in the 70s/80?

Jon Elson elson at
Sat May 11 22:26:15 CDT 2019

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  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.


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