Re: Byte ordering (was: Whether something is RISC or not)

On Thu, 3 Oct 2024 22:17:23 -0000 (UTC)
Lawrence D'Oliveiro <ldo@nz.invalid> wrote:

On Thu, 03 Oct 2024 09:39:03 GMT, Anton Ertl wrote:
 

BTW, at least in my 32-bit PowerPC manual the claim is that PowerPC
is a 64-bit architecture, and that the manual describes only the
32-bit subset.  Maybe the original Power was 32-bit. 

 
I would say IBM designed 32-bit POWER/PowerPC as a cut-down 64-bit
architecture, needing only a few gaps filled to make it fully 64-bit.
 
The PowerPC 601 was first shown publicly in 1993; I can’t remember
when the fully 64-bit 620 came out, but it can’t have been long after.
 

For all practical purposes, PPC/MPC620 never came out.
That is, the chip was formally shipped 2-3 years later than originally
planned in order to fulfill contractual obligations by somebody I don't
remember to somebody else I also don't remember. But that 2nd somebody
barely used it.
By that time, IBM itself had another 64-bit POWER CPU working. That one
had less ambitious microarchitecture than 620, but also had one advanced
feature that didn't appear in "big" POWER CPUs until POWER5 7 years
later - multi-threading.

https://en.wikipedia.org/wiki/IBM_RS64

Motorola did a similar thing with the 68000 family: if you compare
the original 68000 instruction set with the 68020, you will see the
latter only needed to fill in a few gaps to become fully 32-bit.
>

Not similar at all.

Compare this with the pain the x86 world went through, over a much
longer time, to move to 32-bit.

As far as Intel is responsible, only one year longer - 8 years vs 7
years.
And if we count only main line CPUs then it would be 8 years vs 8 years
(from POWER to POWER3).