ENIAC runs at the University of Pennsylvania
Eighteen thousand vacuum tubes replace a room of human 'computers' calculating artillery tables
Quick facts
- Built by
- J. Presper Eckert and John Mauchly, University of Pennsylvania
- Dedicated
- 15 February 1946
- Vacuum tubes
- More than 17,000
- Original purpose
- Artillery firing table calculations for the U.S. Army
What happened
J. Presper Eckert and John Mauchly led a team at the University of Pennsylvania's Moore School of Electrical Engineering building ENIAC, the Electronic Numerical Integrator and Computer, starting in 1943 to calculate artillery firing tables for the Army. It first ran in late 1945 and was formally dedicated on 15 February 1946. Using more than 17,000 vacuum tubes as electronic switches, ENIAC could execute conditional branches, letting it change its calculation path based on prior results, an 'if this, then that' capability that made it reprogrammable rather than fixed to one task. Reprogramming meant physically rewiring plugboards and setting switches, which could take days, but the machine itself performed calculations thousands of times faster than any electromechanical predecessor.
Why it matters
ENIAC is generally treated as the first general-purpose electronic digital computer, the point where computing left electromechanical relays behind for good. Its slow, physical reprogramming process is exactly the problem the stored-program concept, developed in parallel by the same Moore School team, was built to solve.
How we know
Penn Engineering's own historical account of ENIAC, published for its 80th anniversary, describes the build, the vacuum tube count, and the conditional-branching capability directly from the university's institutional record.
Sources
- Penn Engineering, University of Pennsylvania. Penn's ENIAC, the World's First Electronic Computer, Turns 80 · Reputable sourceengineering.upenn.edu · The domain "engineering.upenn.edu" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
- IEEE Spectrum. ENIAC, the First General-Purpose Digital Computer, Turns 80 · Peer-reviewedspectrum.ieee.org · The domain "spectrum.ieee.org" is on our Peer-reviewed registry. · Link is live and its text matches the event's key terms (Jul 2026)
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