From owner-pups@minnie.cs.adfa.edu.au Wed Sep  8 10:04:59 1999
Received: (from major@localhost)
	by minnie.cs.adfa.edu.au (8.9.3/8.9.3) id KAA03094
	for pups-liszt; Wed, 8 Sep 1999 10:02:10 +1000 (EST)
Received: from mpl.ucsd.edu (chiton.ucsd.edu [192.135.238.128])
	by minnie.cs.adfa.edu.au (8.9.3/8.9.3) with ESMTP id KAA03088
	for <pups@minnie.cs.adfa.edu.au>; Wed, 8 Sep 1999 10:02:00 +1000 (EST)
Received: (from cdl@localhost)
	by mpl.ucsd.edu (8.8.8+Sun/8.8.8) id XAA04723;
	Mon, 6 Sep 1999 23:04:02 -0700 (PDT)
Date: Mon, 6 Sep 1999 23:04:02 -0700 (PDT)
From: Carl Lowenstein <cdl@mpl.ucsd.edu>
Message-Id: <199909070604.XAA04723@mpl.ucsd.edu>
To: pups@minnie.cs.adfa.edu.au, wkt@cs.adfa.edu.au
Subject: Re: Diff between 11/20 and 11/45?
Sender: owner-pups@minnie.cs.adfa.edu.au
Precedence: bulk

> From: Warren Toomey <wkt@cs.adfa.edu.au>
> Subject: Diff between 11/20 and 11/45?
> To: pups@minnie.cs.adfa.edu.au (Unix Heritage Society)
> Date: Tue, 7 Sep 1999 09:56:09 +1000 (EST)
> 
> 	Dennis Ritchie has unearthed some really old Unix a.out
> executables from around 1st Edition - 2nd Edition period: see
> Distributions/research/1973_stuff in the PUPS Archive.
> 
> These executables were written for a PDP-11/20. Are there any significant
> USER-MODE differences between the 11/20 and later PDP-11 models? I'm
> thinking missing instructions, different addressing mode behaviour etc.

There's a good table in the back of the more recent micro-11 manuals.

The first genuine user-mode difference that I remember coming across was
an incompatibility in the result of

	MOV SP, -(SP)

It isn't really clear to me why one would want to use this particular
instruction, however it turned out to hang both BASIC and FOCAL at the
time.  A zero-length patch wasn't too hard to figure out.

    carl

        carl lowenstein         marine physical lab     u.c. san diego
        {decvax|ucbvax} !ucsd!mpl!cdl                 cdl@mpl.ucsd.edu
                                                  clowenstein@ucsd.edu

