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From: dave@enmasse.UUCP (Dave Brownell)
Newsgroups: net.micro.atari
Subject: Re:  Unix without an MMU
Message-ID: <520@enmasse.UUCP>
Date: Thu, 9-Jan-86 21:45:47 EST
Article-I.D.: enmasse.520
Posted: Thu Jan  9 21:45:47 1986
Date-Received: Sat, 11-Jan-86 08:08:27 EST
References: <8601071721.AA03900@ucbvax.berkeley.edu> <11372@ucbvax.BERKELEY.EDU>
Reply-To: dave@enmasse.UUCP (Dave Brownell)
Organization: Enmasse Computer Corp., Acton, Mass.
Lines: 16

It was recently asserted here that UNIX runs on the IBM PC without an
MMU.  Well ... sort of.

The segment registers can be used as an MMU, if you keep programmers
from using them.  Since that can't really be done on an 8086/88, PC/IX
(and VENIX, Xenix, ...) on IBM PCs doesn't really count as secure.
(Ergo it's not UNIX.)  Processes can mangle each other at will.

In short, it's not really UNIX there, and it pretty much DOES have an
MMU.  Better than nothing, but I wouldn't buy it.  UNIX needs at LEAST
memory mapping.  This can be real cheap!  but the 520ST doesn't have it.

-- 
David Brownell
EnMasse Computer Corp
...!{harvard,talcott,genrad}!enmasse!dave