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Eckert and Mauchly: Electronic Numerical Integrator And Computer (ENIAC), 1949

Vacuum Tubes and Flip-Flops

Vacuum tubes were a key element of the early success of the electronic age. Vacuum tubes allowed for the easy regulation of electricity, and they functioned like on-off switches. All vacuum tubes, from the simple to the more complex, contained an emitter and a collector. The collector "collected" incoming electricity, and the emitter "emitted" it in forms such as light. The ability to turn on and off very quickly was what inspired John Mauchly to consider the possibility that counting could be accomplished by representing numbers with electrical pulses. These pulses, he hypothesized, could then be controlled and counted with vacuum tubes. Mauchly estimated that using vacuum tubes in this manner would enable calculations to be performed in roughly two-hundredths of a second: much faster than calculations performed by the Differential Analyzer. Vacuum tubes would become a critical component of ENIAC, and the completed ENIAC would contain nearly 18,000!

Another key element of the success of the electronic age was the flip-flop. Designed in Bell Telephone Labs by research mathematician George M. Stibitz, flip-flops were circuits of relays that could count based on the flow of electricity. The circuit had lamps that glowed for the digit 1 and were dark for the digit 0. It coded traditional base-ten numbers as a series of 1s or 0s. In ENIAC, flip-flops composed of vacuum tubes enabled the first computer to represent numbers electronically.

Taken in the 1940s, the photograph at right zooms in on the complex design of the ENIAC.