Re: The Design of Design

John Levine <johnl@taugh.com> schrieb:

S/360 invented eight bit byte addressed memory with larger power of 2
data sizes, which I think all by itself is enough to explain why it
survived. All the others, which were word or maybe decimal digit
addressed, died. Its addresses could handle 16MB which without too
many contortions was expanded to 2GB, a lot more than any other design
of the era. We all know that the thing that kills architectures is
running out of address space.

Brooks wrote that the design was supposed to have been 32-bit
clean from the start, but that the people who implemented the BALR
instruction (which puts some bits of the PSW into the high-value
byte) didn't follow that guideline.  He blamed himself for not making
that sufficiently clear to all the design team.

He also commented on the carefully-designed gaps in the opcode space;
extensibility was designed in from the beginning.  @John S: Another
important point about S/360 you might want to follow, as Mitch
keeps telling you...

I thought the PDP-10 was swell, but even if DEC had been able to
design and ship the Jupiter follow-on to the KL-10, its expanded
addressing was a kludge. It only provided addressing 8M words or about
32M bytes with no way to go past that.

Reading

http://bitsavers.informatik.uni-stuttgart.de/pdf/dec/pdp10/KC10_Jupiter/ExtendedAddressing_Jul83.pdf

I concur that it was a kludge, but at least they seem to have
allowed for further extension by reserving a 1-1- bit pattern,
as an illegal indirect word.

However, one questions.  Designs like the PDP-10 or the UNIVAC
(from what I read on Wikipedia) had "registers" at certain
memory locations.  On the PDP-10, it even appears to have been
possible to run code in the first memory locations/registers.

It seems that the /360 was the first machine which put many
registers into a (conceptually) separate space, leaving them open
to implementing them either in memory or as faster logic.

Is that the case, or did anybody beat them to it?