British mathematician Alan Turing (1912–1954) described what became known as the "Turing Machine" in his 1936 paper, "On Computable Numbers, with an application to the Entscheidungsproblem," which was published in the Proceedings of the London Mathematical Society in early 1937. The machine was actually a concept, not a piece of equipment, but its principles set the stage for the development of digital computers later in the twentieth century.

The machine can be described as a finite state control device (meaning that it has a finite number of states that control its operations), with a tape of unlimited length, divided into squares, upon which symbols may be written or stored. A sequence of actions can take place when a symbol is scanned by a read/write head and the machine is in a certain state. The sequence of actions is the "program."

At any point in time, the...