Xref: utzoo comp.arch:12926 comp.misc:7827
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!cs.utexas.edu!uunet!portal!cup.portal.com!ts
From: ts@cup.portal.com (Tim W Smith)
Newsgroups: comp.arch,comp.misc
Subject: Re: LoadAll?
Message-ID: <25493@cup.portal.com>
Date: 30 Dec 89 07:15:10 GMT
References: <597@unmvax.unm.edu>
Distribution: usa
Organization: The Portal System (TM)
Lines: 18

One good(?) use for LoadAll is to allow real mode access to memory
above 1 meg on a 286 in real mode.  This works because the 286, even
in real mode, uses the base registers associated with DS and ES.
These are normally zero in real mode, and there is no normal way to
change them ( in protected mode, they are updated whenever DS or
ES are changed ).

This comes in real handy for 286 boot code that wants to load a
protected mode operating system, such as Unix, that might not fit
into the first meg, when the boot code must run in real mode because
it wants to use ROM BIOS code that would freak out if the 286
were in protected mode.


On the 386, this is not a problem, since you can simply switch
between real and protected mode in the boot code.

						Tim Smith