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From: jlg@lanl.ARPA
Newsgroups: net.arch
Subject: Re: RMS v/s UNIX (non-religious) -- fun with TM
Message-ID: <23121@lanl.ARPA>
Date: Mon, 11-Mar-85 15:14:06 EST
Article-I.D.: lanl.23121
Posted: Mon Mar 11 15:14:06 1985
Date-Received: Tue, 12-Mar-85 21:29:54 EST
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Organization: Los Alamos National Laboratory
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> > Someone made the claim that there are some issues pertaining to locks that
> > UNIX could not do at all even with libraries.  This is clearly not true
> > since VAX-UNIX can simulate a general Turing machine and can therefore
> > perform ANY computable function.
> 
> Clear as mud...VAX-UNIX can't even simulate all finite automata, much less
> a turing machine.  Does anyone out there have a machine that *can* simulate
> a turing machine?  I want to put one next to my perpetual motion machine :-).

MOST computers can SIMULATE a Turing machine.  The only thing that prevents
them from being computationally equivalent to a Turing machine is the lack
of an infinite store.  But even an infinite store can be SIMULATED by simply
changing the disk packs as they fill.  Theorems of computational equivalence
can (and frequently are) applied to finite systems as well as infinite ones.
Obviously, Turing machine simulation can only proceed as far as your budget
for mass storage allows, but it really IS a simulation of the real thing.
There is a difference between simulation and reality.

J. Giles