Re: Why I've Dropped In

On 6/12/2025 8:00 AM, quadibloc wrote:

On Wed, 11 Jun 2025 17:05:13 +0000, Thomas Koenig wrote:
 

What is the use case for having base and index register and a
16-bit displacement?

 The IBM System/360 had a base and index register and a 12-bit
displacement.

Yes, but as I have argued before, this was a mistake, and in any event base registers became obsolete when virtual memory became available (though, of course, IBM kept it for backwards compatibility).

Most microprocessors have a base register and a 16-bit displacement.
 So this lets my architecture be a superset of both of them.

But your different ISA format, etc. means that it is not a true superset.  That is, any S/360 program would have to be recompiled to run on your architecture.  So it is only for some sort of "conceptual", but not actual compatibility that is only for assembler language programmers (and compiler writers).

Great
selling point,

I suspect that the number of S/360 assembler programs being written these days is asymptotic to zero, so not so much.

and thus I didn't think too hard about whether it is
"needed", because an architecture that instead tries to only provide
genuinely necessary capabilities...
 now forces programmers, used to other systems that were more generous in
one way or another, to change their habits!
 That would presumably spoil sales or ruin the popularity of the ISA.

I don't think so.  And consider how much the other problems that you have been struggling with would become so much simpler if you eliminated the base registers and used those for bits in the instructions for other things.
--
  - Stephen Fuld
(e-mail address disguised to prevent spam)