Random-access Turing machine

In computational complexity, a field of computer science, Random-access Turing machine are an extension of Turing machine used to speak about small complexity classes, especially for classes using logarithmic time, like DLOGTIME and the Logarithmic Hierarchy

Definition

On a Random-access Turing machine there is a special pointer tape of logarithmic space accepting a binary vocabulary. The Turing machine has a special state such that when the binary number on the pointer tape is 'p', the Turing machine write on the working tape the pth symbol of the input.

This let the Turing machine read any letter of the input without taking time to move over the entire input, this is mandatory for complexity classes using less than linear time.

References

• N. Immerman Descriptive complexity (1999 Springer), chapter 5