
Turing machine gallery

The following article is a supplement to the article Turing machine.
Turing machine as a mechanical device.
The Turing machine shown here consists of a special paper tape that can be erased as well as written with a "tally mark". Perhaps the TABLE is made out of a similar "read only" paper tape reader, or perhaps it reads punched cards. Turing's biographer Andrew Hodges (1983) has written that Turing as a child liked typewriters. A "'miraculous machine' -- a mechanical process which could work on Hilbert's decision problem" (Hodges p. 98) had been suggested by G. H. Hardy, one of Turing's teachers. Nevertheless, "His machine had no obvious model in anything that existed in 1936, except in general terms of the new electrical industries, with their teleprinters, television 'scanning', and automatic telephone exchange connections. It was his own invention." (Hodges p. 109)
Davis (2000) says that Turing built a binary multiplier out of electromechanical relays (p. 170). As noted in the history section of algorithm punched or printed paper tape and punched paper cards were commonplace in the 1930s.
Boolos and Jeffrey (1974, 1999) note that "being in one state or another might be a matter of having one or another cog of a certain gear uppermost..." (p. 21).
Turing machine as a "poor mug" inside a box pulling the box along a rail.
This description closely follows Emil Post's "Formulation I" for a "finite combinatory process": a man, equipped with and following a "fixed unalterable set of instructions", moving left or right through "an infinite sequence of spaces or boxes" and while in a box either printing on a piece of paper a single "vertical stroke" or erasing it (Post 1936 reprinted in "Undecidable" p. 289). Post's formulation was the first of its type to be published; it preceded Turing's by a matter of a few months.
Both descriptions—Post's, and Boolos and Jeffrey's — use simpler 4-tuples rather than 5-tuples to define the 'm-configurations' (instructions) of their processes.
A robot carries out the instructions.
This model was suggested by Stone (1972):
Stone uses the robot to develop his notion of algorithm. This in turn leads him to his description of the Turing machine and his statement:
References.
See the main article Turing machine for references.