Re: Why VAX Was the Ultimate CISC and Not RISC

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.