[ProfHewitt]

Actors were developed to synthesize and integrate a whole bunch of things including those mentioned by Alan above.

Additional important influences in addition to SmallTalk-72 [Kay November 1972] were Petri nets, Planner [Hewitt 1969], capability systems [Dennis and van Horn], semaphores [Dijkstra], the lambda calculus, and Scott-Strachey semantics failure to integrate everything using the lambda calculus.

1-way message passing is most important for hardware systems in which there is near certainty that a message will be delivered and there is no need to wait for an acknowledgement of receipt.