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From: anton@mips.complang.tuwien.ac.at (Anton Ertl)
Newsgroups: comp.arch
Subject: Re: is Vax addressing sane today
Date: Mon, 07 Oct 2024 08:00:03 GMT
Organization: Institut fuer Computersprachen, Technische Universitaet Wien
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Message-ID: <2024Oct7.100003@mips.complang.tuwien.ac.at>
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jgd@cix.co.uk (John Dallman) writes:
>In article <2024Oct5.191047@mips.complang.tuwien.ac.at>,
>anton@mips.complang.tuwien.ac.at (Anton Ertl) wrote:
>
>> >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.
>
>I see where I'm going wrong: I'm trying to talk about the machines
>designed to run MS-DOS and later Windows, not just the CPUs. The vast
>range of hardware that all had substantial degrees of compatibility as
>regards booting, busses and so on. Those things let their manufacturers
>compete for the DOS and Windows market, whereas x86-based machines that
>weren't PC-compatible only succeeded in quite specialised niches.

There actually were MS-DOS-compatible machines that were not 100% IBM
PC compatible, and did not run programs that used direct hardware
access, but MS-DOS programs that only used BIOS functions (i.e., a
HAL).  The BIOS functions were too slow, so the programs with direct
hardware access won out over those that used the BIOS, and therefore
the 100% IBM PC compatibles won out over the MS-DOS compatibles.

The PC industry then developed a culture of compatibility, and that
helped all OSs, not just DOS and Windows.  E.g., it is much easier to
install Linux on a PC than on some ARM-based SBC; for the ARM-based
SBC the typical way is to use a prepared system image on an SD-card,
because you cannot just put in a USB stick and run an installer.

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