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From: paul@unisoft.UUCP
Newsgroups: comp.arch,comp.sys.nsc.32k,comp.sys.intel,comp.sys.m68k
Subject: Re: Re: Question:  on-chip or off-chip MMU?
Message-ID: <338@unisoft.UUCP>
Date: Tue, 28-Apr-87 12:58:16 EDT
Article-I.D.: unisoft.338
Posted: Tue Apr 28 12:58:16 1987
Date-Received: Thu, 30-Apr-87 05:49:49 EDT
References: <5635@shemp.UCLA.EDU> <122@motsj1.UUCP> <2581@intelca.UUCP>
Reply-To: paul@unisoft.UUCP (Paul Campbell)
Organization: UniSoft Systems; Berkeley, CA
Lines: 28
Xref: utgpu comp.arch:1077 comp.sys.nsc.32k:125 comp.sys.intel:199 comp.sys.m68k:407

In article <2581@intelca.UUCP> clif@intelca.UUCP (Clif Purkiser) writes:
>
>After reading some 68030 articles I was under the impression that
>the 030 implemented a subset of the 68851, perhaps I am wrong.  
 .....
>
>-- 
>Clif Purkiser, Intel, Santa Clara, Ca.
>{pur-ee,hplabs,amd,scgvaxd,dual,idi,omsvax}!intelca!clif
>

	While it is true that the PMU is a superset of the 68030 this is in
practice not a problem, for Unix kernels anyway, it turns out that the stuff
in the PMMU that is not in the 68030 is not generally used by Unix kernels
(the accent here is on UNIX kernels, other [ring protection domain based kernels
for example] might use them, or sophisticated debuggers). One of the reasons
for this is that early on everyone had to have MMB compatability (there were no
PMMUs) and all those extra goodies weren't there. In our PMMU/MMB kernels when
we did the MMU code we had no 68030 docs to guide us (just rumors, mostly
untrue) and the result was something that will port to a 68030 with less than a
week's work. I think that the 68030 being a subset of the PMMU is a non issue,
for Unix anyway.

	"68030, what me worry?"

	Paul Campbell
	UniSoft Systems
	..!ucbvax!unisoft!paul