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From: tim@ism780c.UUCP (Tim Smith)
Newsgroups: comp.arch,comp.sys.nsc.32k,comp.sys.intel,comp.sys.m68k
Subject: Re: Question:  on-chip or off-chip MMU?
Message-ID: <6047@ism780c.UUCP>
Date: Thu, 23-Apr-87 16:22:06 EST
Article-I.D.: ism780c.6047
Posted: Thu Apr 23 16:22:06 1987
Date-Received: Sat, 25-Apr-87 14:47:58 EST
References: <5635@shemp.UCLA.EDU>
Reply-To: tim@ism780c.UUCP (Tim Smith)
Organization: Interactive Systems Corp., Santa Monica CA
Lines: 23
Xref: mnetor comp.arch:1084 comp.sys.nsc.32k:114 comp.sys.intel:191 comp.sys.m68k:397

In article <5635@shemp.UCLA.EDU> fan@CS.UCLA.EDU (Roy Fan) writes:
>	Question 1 :  are there any other factors that might affect the
>design of the MMU being on-chip or off-chip?

I read a claim somewhere that said that it is better to use the on-chip
space for floating point, and make the MMU external, rather than have an
on-chip MMU and an off-chip floating point unit.

The argument was that you have to go off chip anyway to access memory,
so it should be possible to make an external MMU as efficient as an
internal one, whereas external floating point will be much slower than
internal floating point.

I have no idea if this is right or not.

I prefer an internal MMU because then the system designer can't leave
it out!  I can deal with missing floating point in software.  I can't
deal with a missing MMU in software.
-- 
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