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Turing machine: Be familiar with the structure and use of Turing machines that perform simple computations. 62 Know that a Turing machine can be viewed as a computer with a single fixed program, expressed using: • a finite set of states in a state transition diagram • a finite alphabet of symbols • an infinite tape with marked-off squares • a sensing read-write head that can travel along the tape, one square at a time. One of the states is called a start state and states that have no outgoing transitions are called halting states. Exam questions will only be asked about Turing machines that have one tape that is infinite in one direction. Understand the equivalence between a transition function and a state transition diagram. Be able to: • represent transition rules using a transition function • represent transition rules using a state transition diagram • hand-trace simple Turing machines. Be able to explain the importance of Turing machines and the Universal Turing machine to the subject of computation. Turing machines provide a (general/formal) model of computation and provide a definition of what is computable.

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Topic

A model of computation

Subtopic

Turing machine

Aqa A Level Computer ScienceTheory of computation

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Quick explanation

Turing machine: Be familiar with the structure and use of Turing machines that perform simple computations. 62 Know that a Turing machine can be viewed as a computer with a single fixed program, expressed using: • a finite set of states in a state transition diagram • a finite alphabet of symbols • an infinite tape with marked-off squares • a sensing read-write head that can travel along the tape, one square at a time. One of the states is called a start state and states that have no outgoing transitions are called halting states. Exam questions will only be asked about Turing machines that have one tape that is infinite in one direction. Understand the equivalence between a transition function and a state transition diagram. Be able to: • represent transition rules using a transition function • represent transition rules using a state transition diagram • hand-trace simple Turing machines. Be able to explain the importance of Turing machines and the Universal Turing machine to the subject of computation. Turing machines provide a (general/formal) model of computation and provide a definition of what is computable

  • This point belongs to A model of computation, especially Turing machine.
  • You need to be able to turing machine: Be familiar with the structure and use of Turing machines that perform simple computations. 62 Know that a Turing machine can be viewed as a computer with a single fixed program, expressed using: • a finite set of states in a state transition diagram • a finite alphabet of symbols • an infinite tape with marked-off squares • a sensing read-write head that can travel along the tape, one square at a time. One of the states is called a start state and states that have no outgoing transitions are called halting states. Exam questions will only be asked about Turing machines that have one tape that is infinite in one direction. Understand the equivalence between a transition function and a state transition diagram. Be able to: • represent transition rules using a transition function • represent transition rules using a state transition diagram • hand-trace simple Turing machines. Be able to explain the importance of Turing machines and the Universal Turing machine to the subject of computation. Turing machines provide a (general/formal) model of computation and provide a definition of what is computable.
  • Use the linked flashcards and practice questions to check recall, then practise applying the idea in an exam-style answer.

Why it matters

This objective helps connect Turing machine to exam-style questions, flashcards, and revision notes for A model of computation.

Quick student answer

Which combination correctly describes the main components of a Turing machine?

Direct answer

A finite set of states, a finite alphabet, an infinite tape and a sensing read-write head

Key terms

  • Transition function: A formal representation of the rules that specify how a Turing machine changes state, writes a symbol and moves its head in response to the current state and symbol read.
  • Computable: Describes a task that can be performed by a suitable Turing machine.

Common trap

Confusing the symbol read with the symbol written: Read the rule in order: identify the current state and symbol read, then apply the new state, write the specified symbol and move in the specified direction.

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