What are X-Machines?
Mike Holcombe · Formal Aspects of Computing · 2000
Abstract. X-machines were introduced by S. Eilenberg in 1974 ([Eil74]) as a mathematical framework for examining the relationships between languages and automata. The X-machine definition provided a very general concept that captured in a simple and elegant way a wide variety of existing models and their computational behaviour. Thus finite state machines, pushdown automata and Turing machines all provided different examples of X-machines obtained by varying some of the components of the X-machine's definition.