1.0. Halfword overflow?

posted Sep 14, 2010, 7:27 AM by Jeff Ogden   [ updated Sep 29, 2010, 7:24 AM ]
It wasn't a Y2K issue exactly, but one MTS date and time issue that is widely mentioned on the Web had to do with a halfword integer overflow first encountered by the folks at NUMAC.

From Computer-Related Risks: Excerpts on Computer Calendar-Clock Problems, Peter G. Neumann, Computer Science Laboratory, SRI International:

Overflows. The number 32,768 = 215 has caused all sorts of grief that resulted from the overflow of a 16-bit word. ...  Brian Randell reported that the University of Newcastle upon Tyne, England, had a Michigan Terminal System (MTS) that crashed on 1989 Nov 16, 215 days after 1900 Mar 01. Five hours later, MTS installations on the U.S. east coast died, and so on across the country, an example of a genuine (but unintentional) distributed time bomb.

I'd left the UM Computing Center for Arbortext when this took place, but I heard about it. The story I remember was a little different. It was that the five to eight hour time difference between Newcastle and sites in North America allowed the Newcastle folks to spread the word and get the North American MTS systems patched in time to avoid the problem. Is my memory any good or is this just wishful thinking on my part?

Tony Young included this ps on a note that he sent me back in August:
I'm sure MTS anecdotes are totally inappropriate to your article, but do you remember the 31-bit MTS date overflow problem - perhaps one of the few advantages of having MTS systems in England who hit the problem some 5(6?) hrs earlier and were able to give early warning?

Anecdotes may have been inappropriate for the Wikipedia article, but they are just the thing for this web site.

And George Helffrich sent me this note yesterday (13Sep2010):
I don't think the system crashed; I think it was *FILESAVE that was unavailable due to 16 bit integer days in the directory of file versions saved.  It would be interesting to unearth newsletters to see what actually happened.  Viktors Berstis would probably remember; he wrote the original code, though had left for IBM by then.

There are copies of the MTS Newsletters at UM's Bentley Historical Library, so I can check them there. But I'm guessing that by 1989 this would have been recorded in CONFER, *FORUM, or sent via e-mail and not included in the paper newsletter, if we were still publishing the paper version in 1989.

Does anyone know where we can find Brian Randell's initial report?  Or does anyone remember the details of this event?


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