An automaton is conceived as a theoretical device which reads and accepts symbols in its vocabulary V from a tape consisting of cells (one per symbol), and moves along the tape, according to a set of instructions (transitions); some automata are equipped with memory for this purpose. Automata are said to accept languages, formal grammars are said to generate languages; equivalences in respect of languages accepted or generated were defined by Chomsky in the late 1950s between automata and formal grammars.
In computational phonology, practically the only kind of automaton which is relevant is the Finite State Automaton.