ENIAC, completed in 1945, was one of the first general-purpose electronic computers. About how many vacuum tubes did it use?
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Answer
About 18,000 vacuum tubes
It weighed nearly 30 tonnes and filled a large room, and its early programmers were six women who had to rewire it by hand for each new problem.
How to estimate it
ENIAC worked in decimal. It had 20 accumulators, each storing a 10-digit number. Every digit needed a ring of 10 flip-flops of 2 tubes each, plus gating, about 50 tubes per digit. 20 × 10 × 50 = 10,000 tubes for storage alone. The multiplier, divider, function tables and control units roughly doubled that: 20,000. The real count was about 18,000 vacuum tubes.
Source: US Army; Smithsonian Institution; Penn Engineering
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