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From: Thomas Koenig <tkoenig@netcologne.de>
Newsgroups: comp.arch
Subject: Re: Why VAX Was the Ultimate CISC and Not RISC
Date: Thu, 6 Mar 2025 06:53:23 -0000 (UTC)
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EricP <ThatWouldBeTelling@thevillage.com> schrieb:

>> 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.
>
> MMI's PAL Programmable Array Logic is a subset of a Programmable Logic Array.
> PAL has programmable AND matrix but a fixed OR matrix.
> PLA has both AND and OR matrix programmable.
>
> Mask programmed PLA's were available since 1970, and field programmable
> FPLA's available in 1976 from a number of suppliers (e.g. Signetics).
> https://en.wikipedia.org/wiki/Programmable_logic_array

I read somewhere that these were not used much because, in the
beginning, they were slow, big, expensive and difficult to program.

This is probably why they were not considered as a replacement for
the PAL chips for the MV/8000, had MMI failed - they were not up
to the job.

> If one was building a RISC style ISA cpu in 1975 they could be used
> for decoding and state machines for fetch, load/store, page table walker.
> I don't know the price.

They could have been used for the same things on the VAX 11/780.  Does
anybody know if they were?