SemiOT: Mourning for Classic Computing

From: Richard Erlacher <edick_at_idcomm.com>
Date: Tue Aug 21 09:49:14 2001

----- Original Message -----
From: "Iggy Drougge" <optimus_at_canit.se>
To: "Tony Duell" <classiccmp_at_classiccmp.org>
Sent: Monday, August 20, 2001 8:11 PM
Subject: Re: SemiOT: Mourning for Classic Computing


> Tony Duell skrev:
>
> >> I take it you're no big fan of load/store designs?
>
> >Actually, load/store architectures do tend to have a large number of
> >internal CPU registers, and those registers tend to be general-purpose.
> >Which means I have no real problem with them.
>
> There must be two load/store designs, then; those which rely on fast memory
> access, and those which don't, yet rely upon it and compensate through a large
> number of registers. The 6502 would belong to the first case.
>
<snip>

> But then again, that's a lot of registers compared to the 6502. And they're
> not as flexible as the 68000 set of registers, AFAIK.
> Tell me, are there any common eight-bitters with more registers than the 6809?
>
The Z-80 has MORE registers, first of all because it has two complete sets ...
but then it's of an earlier generation than the 6809 and 68K, which are of more
or less the same generation but targeted at different markets. The 6502, BTW,
though it's of an earlier generation than the 6809, is capable of significantly
higher performance, again based on the technology in which it was originally
designed and implemented, because, since it was so small and thrifty,
internally, it could be run at much higher speeds than the much later 6809. In
order to capitalize on the higher speed of the cpu, however, it did require
faster RAM. This made the zero-page registers particularly interesting in the
context of an extended register set, since, in a single instruction, albeit with
multiple cpu cycles, it could access data stored there about as fast as any
other CPU could access internal resources. It wasn't terribly unusual to see a
6502 that used memory at different rates, depending on location in the memory
map. Consequently, it was possible to run programs that lived in lower memory
at high speed without having a large amount of fast memory.

The 6809 was targeted at more computing-intensive applications than was the
prevous generation of processors, however, and, therefore, could do things more
"elegantly" from a computer-science standpoint. If there had been an integrated
MMU it would have been a major challenger to the 8xx86 series with its awkward
segment scheme. The latter, however, did have a real 16-bit architecture,
however.

With its two-of-everything register set, the Z80 definitely had more registers
internally than the 6809, though.

Dick

> --
> En ligne avec Thor 2.6a.
>
> Iggy tipsar: Vill du l?sa en PDF-fil, men saknar l?sare, skicka den till
> pdf2txt_at_adobe.com, du f?r den tillbaka som ren ASCII till din epostadress.
>
>
Received on Tue Aug 21 2001 - 09:49:14 BST