Re: Diff between 11/20 and 11/45? - TUHS

7 Sep 1999

...
  From: Warren Toomey &lt;wkt(a)cs.adfa.edu.au&gt;
 Subject: Diff between 11/20 and 11/45?
 To: pups(a)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(a)mpl.ucsd.edu
                                                  clowenstein(a)ucsd.edu

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