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# Turing machine

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The Turing Machine is a model of computer execution and storage created by Alan Turing in On Computable Numbers, with an Application to the Entscheidungsproblem (Proceedings of the London Mathematics Society, 1937).

The 'hardware' for the abstract machine involves an infinite tape divided into cells which could contain a symbol. The machine could perform the following operations:

- Move right one cell

- Move left one cell

- Read from a cell

- Write to a cell

- Halt

A Turing machine is comprised of the finite set of instructions which determine the machine's behavior. Each instruction tells the machine what to do, then which instruction to follow next. Each instruction depends on what the machine reads from the current cell. Written out, the set of instructions for a given Turing machines is known as the "standard description." This description can be encoded as an integer, the "description number."

Alan Turing was able to formally define a machine, which he called the universal computing machine, which could take as input the "standard description" of any other Turing machine, and compute the output of that machine. It could thus emulate any other Turing machine. The universal computing machine (also known as the universal Turing machine) can perform any computation that any digital computer would ever be capable of accomplishing.

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Last edited August 15, 2001 5:27 am (diff)
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