Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!psuvax1!eds1!cdh1
From: cdh1@eds1.UUCP (C. Daniel Hassell)
Newsgroups: comp.windows.ms
Subject: Is this real protected mode?
Keywords: Win 3.0
Message-ID: <445@eds1.UUCP>
Date: 13 Jun 90 16:47:42 GMT
Distribution: comp
Organization: EDS - Senate of Pennsylvania
Lines: 33



Well, I sent in the Win 3.0 upgrade coupon and now I wait.
In the meantime, I have a few questions for those of you who actually
have your copies . . .

Does anyone know how the "standard" mode (286) actually works?  The
80286 doesn't have a hardware-based virtual-8086 mode, so Windows must
simply load each program as a regular protected-mode task, and then
proceed to trap and redirect all the interrupts, etc.  Although you
still have a 64K segment limit, 286 protected mode uses 24-bit memory
addresses to get a 16-MB address space.  

But this raises an interesting question.  What would happen if one of
those tasks began direct accesses to more than 1-MB?  After all, if a
DOS program's addresses are interpreted as look-ups into a segment
descriptor table, which contains the true address in 24-bit fashion,
then there is no inherent barrier at 1-MB, even within a task. 
Accessing more memory ought to be only a matter of allocating more 64K
segments for your code or data.

Maybe Windows itself imposes such a barrier to keep order (I hope
not)?  Maybe whatever remains of DOS while running in PM creates the
barrier?

Have I missed something, or is this indeed do-able?

If you can shed some light for a poor, confused soul, I'd appreciate
it.

CD Hassell
cdh1@eds1!EDS.COM
psuvax1!eds1!cdh1