Turing machines were invented by Alan Turing, the father of computer science, in 1936. He wanted to define what an algorithm is in precise mathematical terms. His definition turned out to also be the most useful model of a computer to this date.

A Turing machine consists of a processor and an infinite tape with a "start" space on which symbols can be written or erased. The machine begins when it is fed a tape with zeros and ones already written on it (or it could be blank). The processor first reads the symbol in the "start" space. The processor remembers only one number, called its state. It moves back and forth along the tape, reading and writing symbols and changing its state. At each step in the calculation, the action of the processor depends on only two things: its current state number and the symbol currently...