language. With two infinite stacks the machine is Turing equivalent and can parse any recursive formal language. If the machine is allowed to have multiple tape heads, it can parse any language in L or NL, according to whether nondeterminism is allowed. Applications A read-only Turing machine is used in the definition of a Universal Turing machine to accept the definition of the Turing machine that is to be modelled, after which computation continues with a standard Turing machine. In modern research, the model has become important in describing a new complexity class of Quantum finite automata or deterministic probabilistic automata. See also Computability Turing machine equivalents Stack machine Queue automaton Quantum computer References External links Lecture on finite-state automata by Adam Webber Turing machine