Early programmers moved from rewiring machines to stored programs, assembly language, paper tape, and punched-card batch processing.

In 1946, ENIAC and EDVAC engineers J. Presper Eckert and John Mauchly founded a company that became the Eckert-Mauchly Computer Corporation and developed UNIVAC I. During the 1950s, IBM introduced computers including the 701, 704, and mass-produced 650, while Fortran and Lisp helped expand the possibilities of programming. This marked the beginning of widespread commercial computing.

Alan Turing described an abstract machine that clarified what computation could mean. From wartime codebreaking and ENIAC's plugboards to the stored-program designs of EDVAC, ACE, and EDSAC, this episode traces how Turing, John von Neumann, and several engineering teams contributed to the architecture of modern computers.

In the 19th century, Charles Babbage designed pioneering mechanical computers, and Ada Lovelace's notes on the Analytical Engine included an early published computer program and described how a machine could repeat a sequence of operations.