ENIAC was the first electronic general-purpose computer. It was Turing-complete, digital, and capable of being reprogrammed to solve "a large class of numerical problems". When ENIAC was announced in 1946, it was heralded in the press as a "Giant Brain." It had a speed of one thousand times that of electro-mechanical machines.

ENIAC contained 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors and around 5 million hand-soldered joints. It weighed more than 30 short tons (27 t), was roughly 8 by 3 by 100 feet (2.4 m × 0.9 m × 30 m), took up 1800 square feet (167 m2), and consumed 150 kW of power. This led to the rumor that whenever the computer was switched on, lights in Philadelphia dimmed.