High Quality Content by WIKIPEDIA articles! Input/Output Automata provide a formal model, applicable in describing most types of asynchronous concurrent system. On its own, the I/O automaton model contains a very basic structure that enables it to model various types of distributed systems. To describe specific types of asynchronous systems, additional structure must be added to this basic model. The model presents an explicit method for describing and reasoning about system components such as processes and message channels that interact with one another, operating at arbitrary relative speeds. The I/O Automata were first introduced by Nancy A. Lynch and Mark R. Tuttle in "Hierarchical correctness proofs for distributed algorithms", 1987.