Re: is Vax addressing sane today

jgd@cix.co.uk (John Dallman) writes:

In article <2024Oct4.170717@mips.complang.tuwien.ac.at>,
anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:
>

jgd@cix.co.uk (John Dallman) writes:

Linux could not have had the success it did without the large
range of powerful and cheap hardware designed to run Windows.

 
It was first developed on a 386, and many of the early co-developers
also had IA-32 machines.  But the 386 certainly was not designed to
run Windows.  The 386 project was finished before Windows 1.0 was
released in November 1985, and nobody used Windows 1.0 or 2.0, so
why would anybody design a processor for those?  ...

>
OK, "designed to run MS-DOS, and later Windows"?

The 286 protected mode was certainly not designed for MS-DOS, and the
386 paging of linear addresses was certainly not designed for DOS,
either.

The virtual 8086 mode of the 386 was used by Windows/386 (starting
already in 1987).  Was virtual 8086 mode designed into the 386
specifically for Windows?  I doubt it, and AFAIK it is also used by
DOSEMU under Linux, and I expect that you can run, e.g., CP/M-86 on
it.  It seems to be a good idea when designing a CPU like the 386
where backwards compatibility with the 8086 was a requirement.

Can you point to a specific feature of Intel CPUs that you think is
specifically designed in for DOS or Windows?  Even the A20-gate is a
general backwards-compatibility mechanism that may benefit real-mode
software other than DOS.

It seems to me that the 286 protected mode was a continuation of the
iAPX432 ideas, which predated DOS, and that the 386 paging imitated
the virtual-memory mainstream of bigger computing platforms at the
time, such as the VAX and S/370.

And the success of IA-32 and then AMD64 at replacing the RISCs is
exactly because it was not some DOS-centric architecture, but also
provided features needed by other OSs like 386/ix (later Interactive
Unix, which I used myself in 1990 or so), Xenix, Linux, Windows NT,
Solaris, the various BSDs, and others.  And the computers built around
these CPUs also provided these features.

- anton
--
'Anyone trying for "industrial quality" ISA should avoid undefined behavior.'
  Mitch Alsup, <c17fcd89-f024-40e7-a594-88a85ac10d20o@googlegroups.com>