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J. Presper Eckert (the man in the foreground turning a knob) served and John Mauchly (center) designed ENIAC to calculate the trajectory of artillery shells. The machine didn't debut until February 1946, after the end of World War II, but it did launch the computer revolution.
ENIAC contained nearly 18,000 vacuum tubes and filled a 1,500-square-foot room. To program it, different accumulators had to be wired to each other.