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From: Lawrence D'Oliveiro <ldo@nz.invalid>
Newsgroups: comp.arch
Subject: Re: Why VAX Was the Ultimate CISC and Not RISC
Date: Tue, 4 Mar 2025 23:27:38 -0000 (UTC)
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On Tue, 04 Mar 2025 10:04:20 GMT, Anton Ertl wrote:

> Lawrence D'Oliveiro <ldo@nz.invalid> writes:
>>
>>On Mon, 3 Mar 2025 17:53:35 -0000 (UTC), Thomas Koenig wrote:
>>
>>> If your aim is small code size, it is better to compare output
>>> compiled with -Os.
>>
>> Then it becomes an artificial benchmark, trying to minimize code size
>> at the expense of real-world performance.
>>
>> Remember, VAX was built for real-world use, not for academic
>> benchmarks.
> 
> And supposedly the real-world constraints at the time made it necessary
> to minimize code size.

Remember, RAM was much more expensive back then.

For comparison, when Data General started their “Eagle” project (as 
chronicled in Tracy Kidder’s book “The Soul Of A New Machine”), which 
finally shipped as the MV/8000, they decided that having a full 32-bit 
address, VAX-style, was unnecessary, so they used some of those bits--4, I 
think--to hold privilege levels.

Overall, they managed to end up with a simpler architecture than VAX. But 
it ran out of address space a little bit sooner.

> In the current discussion we look at how RV32GC might have fared under
> this constraint.

Sure. Except you need a much more complicated and resource-hungry compiler 
than would have been reasonable to run on a VAX back then.