Weighing 30 tons and filled with nearly 18,000 vacuum tubes, ENIAC could perform 5,000 additions per second, a staggering leap from mechanical calculators. Built to compute artillery firing tables, it arrived too late for World War II but ushered in the electronic computing age. Reporters marveled as its lights flickered through calculations that would have taken humans weeks.
Inside a converted room at the Moore School of Electrical Engineering, journalists watched a machine that seemed to think. ENIAC (Electronic Numerical Integrator and Computer) filled a 30-by-50-foot space, drew 150 kilowatts, and reportedly dimmed the lights of West Philadelphia when switched on. Its 17,468 vacuum tubes failed constantly, so engineers pre-tested tubes and left the machine running continuously to reduce thermal stress from power cycling.
The demonstration that day calculated a missile trajectory in 20 seconds, faster than the missile itself would fly. Six women, Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas, and Ruth Lichterman, programmed ENIAC by physically rewiring plugboards and switches, work later recognized as some of the first true computer programming, though the press releases of the day barely mentioned them.
ENIAC's public debut, delayed by wartime secrecy, transformed computing from a classified military tool into a subject of public fascination. Within a decade its architecture and lessons fed directly into commercial computers like UNIVAC, and the vacuum-tube behemoth became the ancestor of every device now sitting in a pocket.
Key people: John Mauchly, J. Presper Eckert, Kay McNulty