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Path: utzoo!utgpu!water!watmath!clyde!rutgers!lll-lcc!ames!hao!murphy
From: murphy@hao.UUCP
Newsgroups: comp.sys.m68k
Subject: binary compatibility on high-end unix systems
Message-ID: <611@hao.UCAR.EDU>
Date: Thu, 30-Apr-87 02:09:37 EDT
Article-I.D.: hao.611
Posted: Thu Apr 30 02:09:37 1987
Date-Received: Fri, 1-May-87 06:46:35 EDT
References: <5635@shemp.UCLA.EDU> <4244@nsc.nsc.com> <1401@ames.UUCP> <354@winchester.UUCP>
Reply-To: murphy@hao.UUCP (Graham Murphy)
Followup-To: Question:  on-chip or off-chip MMU?
Organization: High Altitude Obs./NCAR, Boulder CO
Lines: 33
Keywords: binary MMU

Having recently spent a weekend getting undump to work on an
Integrated Solutions 68020 machine, I would agree that binary
compatibility is not yet a viable possibility for the high-performance
unix machines around. The reason being IS decided to change the format of their
executable files from the Berkeley Vax format. Not unreasonable,
but annoying.

I have two questions regarding MMU's :

1) Why have so many 68020 OEM's gone to their own MMU's instead of using
the Motorola unit, and is it possible that the 68030 might end-up
being ignored for the same reasons (though the applications
are likely to be different) ?

2) Regarding binary compatibility, how does an MMU effect things at all ?
On cpu's with linear addressing, such as the 68020, compilers can, and
do, designate specifc areas for various purposes, (i.e. executable,
data sections etc.) without any regard to real physical memory capability.
It is surely up to the LOADER to take the binary and put it where the
MMU can find it when needed. So long as the executable file has the same format,
only the loader need be MMU, and therefore, device dependent which would hardly
come as a surprise.  What part am I missing ?

Graham Murphy
High Altitude Observatory
National Center for Atmospheric Research

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