80286 Protected Mode Test

Liam Proven lproven at gmail.com
Sun Mar 14 13:53:38 CDT 2021

On Sun, 14 Mar 2021 at 19:37, Guy Sotomayor via cctalk
<cctalk at classiccmp.org> wrote:

> There were many heated discussions in various task forces (this was of
> course IBM) about the next generation OS (to become OS/2) about the
> '286.  First and foremost was how to be able to run DOS programs on the
> '286. Over very vocal opposition, management decided to use "mode
> switching" rather than any of the other techniques.  It should be noted,
> that a significant portion of us advocated abandoning the '286 in favor
> of the '386 to solve this problem.  The argument that management made
> against that approach assumed that OS/2 would be ready in 9 months and
> that the '386 would be late ('386 at the time was about 12-18 months
> away).  It turned out that OS/2 took well over 18 months to develop.

I will say this, Guy, your posts never cease to amaze me and provide
valuable insight!

I was on the sidelines at the time -- at university, reading about
this stuff in the UK computer mags. From outside too it was very
obvious that OS/2 should target the 386. When I started work, I was in
tech support in an IBM value-added reseller -- that's where I learned
about IBMCACHE.SYS, which we talked of a few years back -- and I can
confirm that most PS/2 owners were not at all interested in OS/2. A
handful ran 3Com 3+Share or Netware 2 on PS/2 boxes as the server, but
most 286 PS/2s were workstations. Only the 386 Model 80 sold almost
exclusively as servers. I still have one myself.

> 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.  I gave
> multiple demos to various folks in management but to no avail.  They had
> decided that mode switching as *the* way that OS/2 was going to work.


> I should also note, that the other way to get back to real mode from
> protected mode is via a triple-fault.  What gets me (and I railed on
> Intel when I worked there for a time) that it still existing in the
> architecture even though they have a machine check architecture now
> (which while at IBM pushed Intel to implement for the '386!).


Liam Proven – Profile: https://about.me/liamproven
Email: lproven at cix.co.uk – gMail/gTalk/gHangouts: lproven at gmail.com
Twitter/Facebook/LinkedIn/Flickr: lproven – Skype: liamproven
UK: +44 7939-087884 – ČR (+ WhatsApp/Telegram/Signal): +420 702 829 053

More information about the cctech mailing list