Re: Turing Machine

From: HARNAD Stevan (
Date: Mon Jun 03 1996 - 21:38:48 BST

> From: "Nottingham Andy" <>
> Date: Thu, 23 May 1996 15:12:07 GMT
> A Turing Machine is a theoretical computer designed by Alan Turing in
> the 1930's. It consists of an infinite amount of storage space
> (memory),

The infinite tape is both input/output and memory.

> the ability to access this memory and carry out any
> computational algorithm. An algorithm being the finite number of
> steps needed to solve a problem. An example of an algorithm is the
> quadratic formula or a cooking recipe. There is also the universal
> Turing Machine. The Church-Turing Thesis states that for every
> algorithm there is a Turing Machine capable of carrying it out.
> Turing then goes on to say the there is a single Universal Turing
> Machine which comprises all these Turing Machines and is therefore
> capable of computing any algorithm.
> These Turing Machines are theoretical. The nearest people have been
> able to get to them is finite state machines. The difference between
> these and Turing Machines is that Turing Machines have an infinite
> amount of memory while in reality that is not possible so the finite
> state machines only have a finite amount of memory storage.
> The nearest thing known like a Turing Machine is the human brain,

No, a digital computer is nearest; it's not clear whether the brain is a
Turing Machine.

> when doing a quadratic equation most people will use some algorithm,
> this algorithm can be translated so a computer can follow it thus
> proving it can do what a person can do, and therefore its relevence
> to cognitive psychologists.

Except this has it backwards: The fact that people and computers can
both EXECUTE algorithms does not demonstrate that what's going on in the
human's head is algorithms.

This reply was good on the narrow question of what a Turing Machine is,
but for an A you need to relate that clearly to the themes of the
course, such as what computation is, whether cognition is computation,

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