Path: utzoo!attcan!uunet!cs.utexas.edu!usc!snorkelwacker!spdcc!esegue!johnl
From: johnl@esegue.segue.boston.ma.us (John R. Levine)
Newsgroups: comp.arch
Subject: Re: 68000 prehistory, was IBM PC prehistory
Message-ID: <1990Jan12.042336.6123@esegue.segue.boston.ma.us>
Date: 12 Jan 90 04:23:36 GMT
References: <1576@aber-cs.UUCP> <9308@cbmvax.commodore.com>
Reply-To: johnl@esegue.segue.boston.ma.us (John R. Levine)
Organization: Segue Software, Cambridge MA
Lines: 18

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.  ...

You'd hope so, but you'd be disappointed.  Different MMUs have all made the
code, data, and stack be addressed at different locations.  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.

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.
-- 
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."