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From: dclemans@mntgfx.MENTOR.COM (Dave Clemans)
Newsgroups: comp.sys.atari.st
Subject: Re: ST hard
Message-ID: <954@dclemans.mntgfx.MENTOR.COM>
Date: Wed, 7-Oct-87 12:02:58 EDT
Article-I.D.: dclemans.954
Posted: Wed Oct  7 12:02:58 1987
Date-Received: Sat, 10-Oct-87 17:47:56 EDT
References: <8710011017.AA11188@ucbvax.Berkeley.EDU> <858@atari.UUCP> <2269@mandrill.CWRU.Edu>
Organization: Mentor Graphics, Beaverton OR
Lines: 13
Summary: ST memory system

As I understand it the reason for it being difficult to impossible to add a
full MMU to the current ST's relates to the video screen refresh.  Specifically,
memory accesses made to refresh the screen happen over the SAME bus as memory
                         

This is normally invisible to you, as on the ST the cpu only needs 50% of the
available memory bandwidth, and the video system also only needs 50%.  But
nothing is left over for extra or longer "cpu" type accesses.

The best way to add an mmu would probably be to speed up the memory system
bandwidth by some fraction, and probably also speed up the cpu clock.

dgc