 Turing first formulated the notion of a general theory of computing along these lines. He proposed abstract machines that operate on infinite tapes with three symbols: blank \((b)\), zero \((0)\) and one \((1)\). Consequently the data domain for Turing machines is the set of relevant tape configurations, which can be associated with the set of binary strings, consisting of zero’s and one’s. The machines can read and write symbols on the tape and they have a transition function that determines their actions under various conditions. On an abstract level Turing machines operate like functions. 