Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10.2 9/18/84; site cornell.UUCP
Path: utzoo!watmath!clyde!burl!ulysses!mhuxr!ihnp4!houxm!vax135!cornell!jqj
From: jqj@cornell.UUCP (J Q Johnson)
Newsgroups: net.arch
Subject: Re: RMS v/s UNIX (non-religious) -- fun with TM
Message-ID: <158@cornell.UUCP>
Date: Tue, 12-Mar-85 08:35:28 EST
Article-I.D.: cornell.158
Posted: Tue Mar 12 08:35:28 1985
Date-Received: Wed, 13-Mar-85 01:08:27 EST
References: <23048@lanl.ARPA> <731@unmvax.UUCP>
Reply-To: jqj@gvax.UUCP (J Q Johnson)
Organization: Cornell Univ. CS Dept.
Lines: 23

>...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 :-).

As with most things, it depends on your precise definitions.  I
consider my VAX/UNIX machine to be a Turing machine since it has a tape
drive and the possibility of adding more modern mass storage devices as
they are developed.  I figure that I can always hang another tape if
necessary (perhaps waiting while the manufacturer makes more tapes for
me), thereby giving me an infinite-tape Turing machine.  Note that a
very simple program for a Turing machine (one that reads n positions
on the tape then rewinds) may for large n take quite a while to
complete since I might need a large piece of the mass of the Universe
as the raw material for the MANY tapes required.  Assumptions:  1/ I
have good field service technicians who can keep my VAX running for an
arbitrarily long time, and 2/ either the mass of the Universe is
infinite or there is no limit on inventable recording densities (since
I need to be able to store a finite but unbounded amount of
information).

Now that I've given you a Turing machine, would you consider a satellite
as a candidate for a perpetual motion device (not a machine since getting
useful work out of it would make it non-perpetual)?