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From: dave@heurikon.UUCP (Dave Scidmore)
Newsgroups: net.micro,net.arch
Subject: Re: What if IBM used a 68000
Message-ID: <142@heurikon.UUCP>
Date: Mon, 25-Nov-85 19:49:01 EST
Article-I.D.: heurikon.142
Posted: Mon Nov 25 19:49:01 1985
Date-Received: Wed, 27-Nov-85 05:42:29 EST
References: <212@fas.ri.cmu.edu>
Organization: Heurikon Corp., Madison WI
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Xref: watmath net.micro:12857 net.arch:2173

> 	*	Ignoring the abortive 68451, Motorola did not even
> 		produced an external VLSI MMU until 1985 (does it work
> 		even now ?).  When it came time to put XENIX on the
> 		9000, a separate board full of LSI was required,
> 		substantially driving up the cost.  The 8088 came with
> 		MMU on board.

Three points:

     1) Our company has been very successfully using the "abortive" 68451
	in our UNIX based products for two and one half years. It does, and
	always has, worked exactly the way the documentation says it should.

     2) The 8088 has *no* MMU at all. It has a segmentation scheme that
	amounts to little more than a simple memory map. The 8088s segment
	register scheme has nothing approaching the features an MMU needs
	to support a multitasking, multiuser operating systems like UNIX.

     3) If you don't know what you are talking about, don't get involved in
	technical discussions.

						Dave Scidmore