The machine was huge, weighing 30 tons, using 200 kilowatts of electric power and contained over 18,000 vacuum tubes, 1,500 relays, and hundreds of thousands of resistors, capacitors, and inductors.
Gradnjo sta nadzorovala John Mauchly in J. Presper Eckert na Univerzi v Pennsylvaniji (University of Pennsylvania); ENIACova razvoj in izgradnja sta trajala od 1943 do polne operativnosti konec 1945.