From:	Christopher Croughton <crough45 AT amc DOT de>
Message-Id:	<97Sep24.084945gmt+0100.11649@internet01.amc.de>
Subject:	Virtual 86 mode (DOS boxes in 32 bit systems)
To:	opendos AT delorie DOT com
Date:	Wed, 24 Sep 1997 07:55:10 +0100
Mime-Version:	1.0

This is slightly off-topic (although not as much so as VAXen <g>),
but I suspect some people here may have knowledge of the subject.

This is a follow-on from discussions about 32-bit DOS possibilities.
What I actually want is a layer on top of DOS which provides multiple
DOS sessions, in the same sort of way as DesqView.  DV does this using
the old EMS calls to map memory into part of the address space, leaving
the bottom part common.  This is not only a security risk but means
that the free memory is much reduced (typically around 550K or less in
each DOS session).

Windows does this another way, it uses the Virtual 86 mode of the 
processor, and so effectively isolates each session from each other
and also typically gives over 600K free.  But Windows has loads of 
other baggage (the GUI for a start) which I don't want.

What I'd like to do is write my own equivalent, but I don't know
enough about the V86 mode to do it.  Heck, I know little about it 
other than it exists!  I'd like it to use 'pure' DPMI 0.9 services
if that can be done.

So my question:  does anyone have experience with this which they 
could share with me?  Is there "prior art" available in the form of 
source?  Does what I want even already exist?

If there's a mailing list which deals with this, please tell me - I 
don't have access to newsgroups at present.

Someone is bound to say "why put it on top of DOS instead of having
its own OS?", so I'll answer it.  A lot of the problems developing an 
OS is that you have to have a lot of the work done before you can
even test it - video and keyboard drivers, disk drivers, etc.  By 
using DOS underneath I can avoid that and go straight to the part
which is new (DOS works fine for those things) and use the "prior
art" without having to reinvent it.  And ideaslly it should run with 
no problems on top of any of the DOSes with nothing but a DPMI driver.

Thanks,
    Chris C

(BTW, if I do come up with anything it will be 'free' in at least the
GNU sense - it may not be GPL (see my other comments on that subject)
but I'm willing to make source available as with all my software...)

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