Like any big invention, the ENIAC was made possible by the contributions of many people who came before it.

John Atanasoff designed a machine that used vacuum tubes to do calculations. Mauchly visited with Atanasoff for several days, and studied the plans for the device. Mauchly realized that the idea of using vacuum tubes for electronic calculating could be expanded into a general purpose computing machine.

Irvine Travis was working on the idea of "ganged calculators"--where the output of several calculators is used as the input of another calculator. He was not able to connect together mechanical calculators to work as he wanted, but his ideas were adopted by the designers of the ENIAC.

These two ideas were brought together in the person of John Mauchly, who envisioned a huge, electronic (vacuum tube), ganged calculator that could do general problems.

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