Universal Turing machine (nonfiction)

A Universal Turing machine U. U consists of a set of instructions in the table that can “execute” the correctly-formulated “code number” of any arbitrary Turing machine M on its tape. In some models, the head shuttles back and forth between various regions on the tape. In other models the head shuttles the tape back and forth.

In computer science, a Universal Turing machine (UTM) is a Turing machine that can simulate an arbitrary Turing machine on arbitrary input.

The universal machine essentially achieves this by reading both the description of the machine to be simulated as well as the input thereof from its own tape.

Alan Turing introduced this machine in 1936–1937.

This model is considered by some (for example, Martin Davis (2000)) to be the origin of the stored program computer—used by John von Neumann (1946) for the "Electronic Computing Instrument" that now bears von Neumann's name: the von Neumann architecture.

It is also known as universal computing machine, universal machine (UM), machine U, U.

In terms of computational complexity, a multi-tape universal Turing machine need only be slower by logarithmic factor compared to the machines it simulates.