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From: valley@gsbsun.uchicago.edu (Doug Dougherty)
Newsgroups: comp.os.msdos.programmer
Subject: Re: Protected mode/Real mode switching
Message-ID: <1991Apr26.160753.4754@midway.uchicago.edu>
Date: 26 Apr 91 16:07:53 GMT
References: <1991Apr15.160333.8107@msuinfo.cl.msu.edu> <37390009@hpopd.pwd.hp.com> <3199@bimacs.BITNET> <1448@balrog.ctron.com>
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dj@ctron.com (DJ Delorie) writes about the 286 LOADALL instruction:

>There is such an opcode, and Microsoft used it in OS/2 for 286
>machines.  From what they told me, they had a really hard time getting
>Intel to tell *them* about it.  They used it primarily to set up the
>hidden portion of the segment registers in real mode to access memory
>above 1M.  It is *not* available on the 386, and may not exist on new
>286 designs, or on non-Intel 286's.  It's very non-portable, also.

I've heard others claim that there is no 386 LOADALL as well.
However, I have a document (available upon request) that purports to
describe the 386 version of LOADALL; apparently it is only partially a
superset of the 286 version.
		-----------------------------------------
Certainly the use of LOADALL is akin to usage of the undocumented
features of the AAD & AAM instructions; "Undocumented DOS" has a very
good section on the distinction between using undocumented features of
the OS (which they argue is inescapable) and using undocumented features
of the chip (which they claim is inexcusable).  However, I think if MS
uses it (LOADALL) in their systems (an operating system, no less) that that
pretty much legitimizes it.  Can you imagine some clone 286 manufacturer
having to admit that their chips won't run OS/2?
--

	(Another fine mess brought to you by valley@gsbsun.uchicago.edu)