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Turing Machine

The Turing Machine was first described by Alan Turing in his 1936 paper On Computable Numbers, where he originally called it an "automatic-machine."

A Turing Machine is not intended to be a practical computer but a thought experiment intended to help computer scientists understand the limits of mechanical computation. It is a device that manipulates symbols such as 1's and 0's contained on a strip of tape and, despite its simplicity, can be adapted to simulate the logic of any computer algorithm, thereby simulating the functions of the CPU inside of a computer.

According to Alan Turing's own definition, as written in his 1948 essay Intelligent Machinery, a Logical Computing Machine (aka Turing Machine) consisted of:

"...an infinite memory capacity obtained in the form of an infinite tape marked out into squares on each of which a symbol could be printed. At any moment there is one symbol in the machine; it is called the scanned symbol. The machine can alter the scanned symbol and its behavior is in part determined by that symbol, but the symbols on the tape elsewhere do not affect the behavior of the machine. However, the tape can be moved back and forth through the machine, this being one of the elementary operations of the machine. Any symbol on the tape may therefore eventually have an innings."

Here is an interesting video of a home-made Turing Machine: