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From: magus@drktowr.chi.il.us (Louis Giliberto)
Followup-To: comp.os.coherent,comp.os.linux,comp.os.minix,comp.os.386bsd.questions,comp.os.misc
Newsgroups: comp.os.coherent,comp.os.linux,comp.os.minix,comp.os.386bsd.questions,comp.os.misc
Distribution: world
Subject: Re: Unix OS for 286
X-Newsreader: TIN [version 1.1 PL8]
References: <C5yq8y.2xH@sugar.neosoft.com>
Message-ID: <93042916845@drktowr.chi.il.us>
Organization: DarkTower Software
Date: Thu, 29 Apr 93 21:51:27 CDT
Lines: 34
Peter da Silva (peter@NeoSoft.com) wrote:
: In article <groot.735474426@baukje.idca.tds.philips.nl> groot@idca.tds.philips.nl (Henk de Groot) writes:
: > Minix 1.5 will run fine as a UNIX system on a 286. Of course there is an
: > 64K+64K limit, but that's because its a 286.
: No, that's because it's an 8086. Minix doesn't use protected mode.
Yes Minix uses protected mode, however it uses segmented memory while
the compiler wants a flat address space. So you get one seg for code (I)
and one for data (D), and the compiler just generates offsets.
If you look at a DOS compiler's assembly output, you'll see it goes
through all these shenanigans to have multiple code and data segments
known affectionately as @DATA and @CODE groups.
On a 386 you can work like that, but jack the seg size up to a couple
of gigs. In fact, you can hop to protected mode, change the segment
size to say 512K, then hop to real mode and you'll have 512K segments
under MS-DOS. k00l! Don't waste your money on a 386 DOS-extender
just so you can store a 512K array - use assembly!
Heh.
-Louis
--
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Louis J. Giliberto, Jr. ! magus@drktowr.chi.il.us (send here)
-sysadmin drktowr ! magus@gagme.chi.il.us (forwards to above)
Chicago, IL USA ! lgilibe@math.luc.edu (probably OK)
Home of DarkTower Software ! lgilibe@orion.it.luc.edu (anal-retentive quotas)
! lgilibe@mica.meddean.luc.edu (best luc.edu sys)
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