80286 Protected Mode Test

[Liam Proven]

On Sun, 14 Mar 2021 at 19:37, Guy Sotomayor via cctalk
<cctalk at classiccmp.org> wrote:
>
> At the time I was fairly familiar with the LOADALL instruction.  I had
> modified PC/AT Xenix to use the LOADALL instruction to allow for running
> Xenix programs and multiple DOS programs simultaneously.

Incidentally, I believe that OS/2 1 was not the only 286 OS affected by this.

The development versions of DR's Concurrent DOS 286 could multitask
DOS apps in protect mode on pre-release 286s, but Intel "fixed" the
feature that permitted this in the first shipping version of the
80286, to DR's dismay and horror.

https://books.google.cz/books?id=2y4EAAAAMBAJ&pg=PA17#v=onepage&q&f=false

AIUI the feature was later restored, but customer uncertainty,
together with suddenly-questionable compatibility with all the 286s
out there, killed CDOS 286.

I suspect this is instrumental in why DR took FlexOS and X/GEM down
the RTOS route instead... in which form it survived and a distant
descendant, formerly IBM 4690 OS, is still sold by Toshiba.

-- 
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