Re: 386 instructions

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#449

From: D Spinellis
Date: Wed, 17 Jan 1990 17:21

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In article <1990Jan17.102756.8171@idt.unit.no> torb@grimne.UUCP (Tor Brekke) writes:
>In article <1451@gould.doc.ic.ac.uk> dds@cc.ic.ac.uk (Diomidis Spinellis) writes:
>>Sorry, but the above is not exactly correct.  It is true that most of the
>>386 instructions can be used in the real mode, but the segment limit is
>>still limited to 64K. 
>
>Sorry, byt this is not correct either. It is possible to trick the 386
>into beliving that it's segments are larger than 64K in real mode.
[...]
>If a descriptor i set up
>with a limit larger than 64K and left in one of the segment registers
>when reentering real mode, the processor will still believe that the
>segment has the old size.

Is this a bug of the 386 or a documented feature?  I have not found any mention
of it in the Intel literature.  It sounds very useful, but if it is 
undocumented it might go away in new chip releases.

Diomidis
--
Diomidis Spinellis                  Internet:                 dds@cc.ic.ac.uk
Department of Computing             BITNET:                   dds@cc.ic.ac.uk
Imperial College                    UUCP:   ...!cernvax!cc.imperial.ac.uk!dds
London SW7 2BZ                      JANET:                    dds@uk.ac.ic.cc

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<13346@garnet.BBN.COM> <580@watserv1.waterloo.edu> <6142@internal.Apple.COM> <8166@portia.Stanford.EDU> <1451@gould.doc.ic.ac.uk> <1990Jan17.102756.8171@idt.unit.no>

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Path: arc1-ca.pugleaf.net!utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!uunet!mcsun!ukc!icdoc!tsun6.doc.ic.ac.uk!zmact61
From: zmact61@tsun6.doc.ic.ac.uk.doc.ic.ac.uk (D Spinellis)
Newsgroups: alt.msdos.programmer
Subject: Re: 386 instructions
Message-ID: <1452@gould.doc.ic.ac.uk>
Date: 17 Jan 90 17:21:18 GMT
References: <13346@garnet.BBN.COM> <580@watserv1.waterloo.edu> <6142@internal.Apple.COM> <8166@portia.Stanford.EDU> <1451@gould.doc.ic.ac.uk> <1990Jan17.102756.8171@idt.unit.no>
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Reply-To: zmact61@doc.ic.ac.uk (D Spinellis)
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