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From: henry@utzoo.UUCP (Henry Spencer)
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: <7976@utzoo.UUCP>
Date: Tue, 28-Apr-87 14:31:45 EDT
Article-I.D.: utzoo.7976
Posted: Tue Apr 28 14:31:45 1987
Date-Received: Tue, 28-Apr-87 14:31:45 EDT
References: <5635@shemp.UCLA.EDU> <122@motsj1.UUCP>, <2581@intelca.UUCP>
Organization: U of Toronto Zoology
Lines: 22

> Contrast this with Unix systems that use processors with off-chip MMUs.
> If I want to buy an application for a 68020 machine I have to specify which 
> machine I am using Apollo, Masscomp etc. Eventhough all of the machines are 
> running Unix-like OS  and use the 68020...

C'mon now, Clif, be fair:  the MMU has virtually nothing to do with this.
The divergences between the various 68020 boxes are in things like object
file formats, system-call conventions, and graphics facilities.  You may
have done a better job on standardizing file formats and call conventions
(although in a couple of years, after the 386 is used more widely, you may
have cause to eat those words), but simply recompiling cures those ills.
The real "porting" problems are things like different graphics hardware
and System V vs. Berklix -- hardly the fault of the MMU.  Actually, in
a different sense they are:  the ugliness of the addressing model on your
previous processors is the reason why you don't have to worry about these
things (yet!), because all the serious divergence took place on better
machines!  Unless you're really clamping down hard on 386 developers, the
same thing will happen to you before too very long.  Welcome to the
32-bit world; hope you like it. :-)
-- 
"If you want PL/I, you know       Henry Spencer @ U of Toronto Zoology
where to find it." -- DMR         {allegra,ihnp4,decvax,pyramid}!utzoo!henry