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

ben bfranchuk at
Sat May 11 19:47:46 CDT 2019

On 5/11/2019 5:14 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?
> Thanks, Warren

8 bit computers are EVIL. REPENT DEAR BROTHER.
24 bit computers are HOLY AND DIVINE.
Building a  12/24 BIT CPU with 8 bit I/O.
(back on topic)

Early 70's computers other than IBM used TTL, and fast
core memory with mostly a 16 bit word width. Other than
the PDP 11, most computers where adapted from the transistor
era with tweaks added for banks of memory.When the late 70's
came around commercial customers had a large main frame computer
or small control computer from a few years earlier with FAST
TTL (S)logic, PDP 11's, IBM 360's or clones,or TTL standard/H like
PDP 8 or NOVA computer.

Bit slice logic like the 2901 alu, (1975) would make for
nice low cost 16/32 bit cpu with byte load/store.
The market for 32 bit computers was decided however
to sell FAST LARGE systems (floating point/64K+ memory)
like the VAX (S TTL) or upgrade other designs like the NOVA computer with
Custom or semi-custom (PAL logic) logic.
INTEL being slow with the forgotten APX 432 design
came out with 8086 leaving us with the defective CPU's
of today.

Ben's view point.

I am doing  my computer with a FPGA development system
for design logic and testing and later using 2901's
and LS TTL with 3 proms used for the alu/control cards.
  I have A nice 8/16/32 cpu design with 512KB of memory
(2901 alu )but I can't get it to route correctly. The 12/24 bit
cpu just fits with the FREE develpment software.
For a few K $ I can get the better version with being able
route by hand my logic to meet timing specs.
Once hardware SD card/serial port and software are working
I then will port the design to TTL.
I may need to write my own tiny langage to boot strap
my system.

16 bit computer format

[op 3..1][ac 3..1][mode 3..1][ix 3..1][aux][k 3..1]
The tricky part is K is the upper 3 address bits
to extend 16 bit offset to 19 bits or a auto indexing
mode. This would be valid memory for the late 70's
early 1980's but not for today.

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