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From: mmm@cup.portal.com (Mark Robert Thorson)
Newsgroups: comp.arch,comp.misc
Subject: Re: LoadAll?
Message-ID: <25528@cup.portal.com>
Date: 31 Dec 89 20:22:53 GMT
References: <597@unmvax.unm.edu> <25493@cup.portal.com>
Distribution: usa
Organization: The Portal System (TM)
Lines: 8

What Tim implied, but didn't say explicitly, was that switching to protected
mode on a 286 is a one-way trapdoor.  Can't get back to real-address mode.
This is why MS-DOS on the 286 must run in real mode (8086 compatibility mode)
because it needs to run 8086/8 binaries.

On the 386, this isn't a problem, because you can switch back to real-mode
after loading the "invisible" part of the segment registers.  This lets you
set up addressing beyond the first 1 Mbytes of address space.