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What is a Turing machine?

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Quick answer

A Turing machine is a simple imaginary computer — a tape of symbols and a head that reads, writes, and moves by following rules — invented by Alan Turing to define what 'computation' means. Anything a real computer can compute, a Turing machine can too.

Key things to understand

  1. An abstract model: an endless tape, a read/write head, and a table of rules.
  2. Despite its simplicity, it can perform any calculation a modern computer can.
  3. It set the theoretical foundation of computer science in 1936.
  4. It defines the very limits of what is computable.
  5. 'Turing complete' means a system is as powerful as a Turing machine.

People also ask

Is a Turing machine a real machine?
No, it's a thought experiment — a mathematical model used to reason about what computers can and cannot do.
What does 'Turing complete' mean?
That a language or system can compute anything a Turing machine can, given enough time and memory.
Why is the Turing machine important?
It precisely defined computation, founding computer science and revealing that some problems can never be solved by any computer.
What is a Turing machine?
An abstract model of a computer that manipulates symbols on a tape by rules, defining what is computable.