Re: Why VAX Was the Ultimate CISC and Not RISC

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?