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From: tmb@mit-prep.ARPA (Thomas M. Breuel)
Newsgroups: net.micro.atari16,net.micro.amiga,net.micro.68k
Subject: Re: 68000 Memory Managment
Message-ID: <71@mit-prep.ARPA>
Date: Fri, 29-Aug-86 12:01:52 EDT
Article-I.D.: mit-prep.71
Posted: Fri Aug 29 12:01:52 1986
Date-Received: Fri, 29-Aug-86 23:26:22 EDT
References: <508@elmgate.UUCP> <64@mit-prep.ARPA> <653@cbmvax.cbmvax.cbm.UUCP> <270@dmsd.UUCP> <7578@tekecs.UUCP>
Reply-To: tmb@prep.UUCP (Thomas M. Breuel)
Organization: The MIT AI Lab, Cambridge, MA
Lines: 19
Keywords: 68000 atari amiga 68k mmu
Xref: mnetor net.micro.atari16:1762 net.micro.amiga:4449 net.micro.68k:1177

||Consider that (for) a simple paging mmu... we are talking under $45 at
||the shelf. This is the difference between the ST being a game machine and
||having the support for process issolation and error detection for a strong
||bussiness machine.
|
|I don't quite buy that.  Look at the #1 business machine -- what kind of MMU
|does it have?  The Atari has just about the same features as the IBM PC --
|including lack of reasonable system software.  The Amiga at least made an
|attempt to make up for the lack of an MMU with good system software.

The IBM PC has a better MMU than the Atari. While segment registers
are awfully annoying if you try to program the 8088 as a machine with
a 20 bit address space, they do provide you with a memory model that
is very similar to the PDP-11 with separate I/D. That is probably 
one of the reasons why there is UN*X for the IBM PC but not for the
Atari. You can achieve a similar effect by using only indexed addressing
on a 68000, but on a 68000 you really lose a lot by doing so.

						Thomas.