Path: utzoo!utgpu!watserv1!watmath!iuvax!mailrus!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.arch
Subject: Re: 68000 prehistory, was IBM PC prehistory
Message-ID: <9324@cbmvax.commodore.com>
Date: 12 Jan 90 16:08:03 GMT
References: <1990Jan12.042336.6123@esegue.segue.boston.ma.us>
Organization: Commodore, West Chester, PA
Lines: 37

in article <1990Jan12.042336.6123@esegue.segue.boston.ma.us>, johnl@esegue.segue.boston.ma.us (John R. Levine) says:

> In article <9308@cbmvax.commodore.com> daveh@cbmvax.commodore.com (Dave Haynie) writes:
>>The MMU is certainly a difference when it comes to implementing UNIX on a
>>680x0 system.  But that's an OS concern, it shouldn't have anything to do
>>with an ABI standard.  ...

> Writing an ABI in which, for example, you don't know whether the data will start 
> at the next 2K boundary after the text or the next 1MB boundary after the text is
> possible but difficult and messy; it forces you to do a lot of relocation at
> exec() time which Unix has not traditionally done.

I really don't know what the AT&T ABI does.  But relocation, even if
necessary, is a trivial thing to support in an object format.  The Amiga OS
stores all objects in a quickly relocatable format, this works just fine. 
It may not be traditional UNIX, but neither is binary compatibility between
vendorrs at any level a traditional feature of UNIX. 

> Since the advent of the 68030, its on-board MMU is the obvious place to
> standardize, but there's a lot of old 68000 crud out there already.

You would certainly hope to support Sun-2s, Sun-3s, Apollo DN660s,
whatever, as well as the newer 68030 compatible boxes.  This sure seems to
me a might simpler than supporting an ABI that gives you '286 compatibility
under a segmented UNIX but still the proper memory paging under the '386
UNIX.  I guess in either case, it points out that designing the ABI right
is a primary concern.  And may also be a good clue as to why the ABI for
things without any installed base or other architectural hair, like 88000
machines, was done by AT&T before 680x0 or 80x86. 

> John R. Levine, Segue Software, POB 349, Cambridge MA 02238, +1 617 864 9650
> johnl@esegue.segue.boston.ma.us, {ima|lotus|spdcc}!esegue!johnl
> "Now, we are all jelly doughnuts."
-- 
Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
                    Too much of everything is just enough