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From: john@anasazi.UUCP (John Moore)
Newsgroups: net.micro.atari
Subject: Re:  Unix without an MMU
Message-ID: <471@anasazi.UUCP>
Date: Sun, 12-Jan-86 09:49:27 EST
Article-I.D.: anasazi.471
Posted: Sun Jan 12 09:49:27 1986
Date-Received: Sat, 18-Jan-86 08:26:08 EST
References: <8601071721.AA03900@ucbvax.berkeley.edu> <11372@ucbvax.BERKELEY.EDU>
Reply-To: john@anasazi.UUCP (John Moore)
Organization: Anasazi, Phoenix Az.
Lines: 33
Summary: We have several - they work

In article <11372@ucbvax.BERKELEY.EDU> ranjit@bugs.UUCP (Ranjit Bhatnagar) writes:
>There are several implementations of UNIX-like operating systems,
>with multitasking, on the MMU-less IBM PC and compatibles.  However
>it is done, it seems to be at least nominally compatible with UNIX.
>What methods are used here?  Could they be applied to a 68000-based
>system?  Am I missing the point entirely?  (Perhaps PC UNIX's
>fork() does NOT act like real UNIX.)
>
>      Ranjit Bhatnagar

We have several Unix systems (not Unix-like) running on the PC. They are
VENIX (Unix V-7), VENIX-V (Unix System V), and PCIX (Unix system 3). These
are all AT&T licensed Unix's and work the same as one other systems (we
also have a CT Megaframe running UNIX System-V, and we port back and forth
all the time).
	However....
	These Unix's DO have the use of limitted MMU capability. The 8086
family has a (disgusting) memory management scheme which uses base registers.
All programs which use less than 64K dataspace are relocatable by simply
changing the contents of the base registers. This is better than absolute
addressing in that even pointers are relocated. It also adds the very
severe limitation of 64K data spaces.
	I agree tha`i MMU's would be nice on the ST. However, it is
possible to make a UNIX (or something very close to it) without
MMU's.

-- 
John Moore (NJ7E/XE1HDO)
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