Jack Dennis is a computer scientist and retired MIT professor. He was involved in early work on time-sharing through the PDP-1 which his research group owned at MIT; that hardware later became famous in computer science history as the machine on which hacker culture started. He also sponsored the MIT student-run Tech Model Railroad Club in its early years, where the hacker culture is said to have taken root before spreading to the MIT Artificial Intelligence Lab.
Later, he was one of the founding members of the Multics project, to which he contributed one of its most important concepts, the single-level memory. Multics, though not particularly commercially successful in itself, was an inspiration for Ken Thompson to develop Unix.
In his teaching at M.I.T. Prof. Dennis developed six subjects in new areas of computer theory and computer systems: (1) Theoretical Models for Computation. The material developed for this subject was published as a book, Machines, Languages, and Computation, written with former graduate students Peter Denning and Joseph Qualitz. (2) Computation Structures. This was the intial version of the basic computer architecture subject of M.I.T.'s undergraduate curriculum in Computer Science.