March 28, 2010

A real turing machine.......

We pay lots of lip service to Turing but has anyone actually seen or thought about what Turing did for computing? Aside from the Turing Test, Alan Turing invented his Machine, a “tape-based” system for digital computing. The machines have always been thought of as a “thought experiment” but on crazy man actually built one.

Although this Turing machine is controlled by a Parallax Propeller microcontroller, its operation while running is based only on a set of state transformations loaded from an SD card and what is written to and read from the tape. While it may seem as if the tape is merely the input and output of the machine, it is not! Nor is the tape just the memory of the machine. In a way the tape is the computer. As the symbols on the tape are manipulated by simple rules, the computing happens. The output is really more of an artifact of the machine using the tape as the computer.

The heart of the turing machine is the read-write head. The read-write head transports the tape and positions cells of the tape appropriately. It can read a cell determining what, if any, symbol is written there. The machine works on, and knows about, only one cell at a time. The tape in my machine is a 1000’ roll of white 35mm film leader. The characters, ones and zeros, are written by the machine with a black dry erase marker.

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