Re: is Vax addressing sane today

Anton Ertl wrote:

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 single most canonical test for IBM PC compatibility was Microsoft's Flight Simulator, taking off from the now demolished Meighs Field in Chicago.
That game used the OS and BIOS for the loading of the game, and then went on to direct hardware access for pretty much the rest of the playing time.

 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.

Terje

 - anton
 

--
- <Terje.Mathisen at tmsw.no>
"almost all programming can be viewed as an exercise in caching"