During the Second World War the computation of artillery firing tables took months; the people doing it — mostly women, whose job title was 'computer' — worked by hand and desk machine. ENIAC, built at the University of Pennsylvania by John Mauchly and J. Presper Eckert, brought the same calculation down to seconds: 17,468 vacuum tubes, thirty tonnes, 150 kilowatts. It ran in 1945 and was presented publicly in 1946.

The machine's limit was not its speed but its reprogramming. Each new computation meant rearranging cables and switches by hand, which took days. The six women who did that work — Kathleen McNulty, Jean Jennings, Betty Snyder, Marlyn Wescoff, Frances Bilas and Ruth Lichterman — are now counted among the first programmers; at the time their names did not appear in the press.

The solution was formulated in the EDVAC report John von Neumann wrote in 1945: instructions are numbers too, so they can be held in the same memory as data. The machine can then read — and even modify — its own program. That arrangement, known as the von Neumann architecture (memory, arithmetic unit, control unit, input/output), is the basic schema of nearly every computer since. Because the report circulated under von Neumann's name alone, the contributions of Eckert and Mauchly were obscured, and the priority argument continues. The idea itself is the physical counterpart of the 'machine that operates on symbols' Lovelace had glimpsed a century earlier.