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A Science Odyssey
People and Discoveries

ENIAC is built

Photo: ENIAC

A bank of blinking lights indicate the mysterious processes going on within: That classic symbol of a computer has lasted long after computers evolved into friendly desktop tools. This was not a dream of science fiction, but a representation of ENIAC (Electronic Numerical Integrator Analyzer and Computer), the gigantic machine credited with starting the modern computer age.

ENIAC, with its 17,468 vacuum tubes, 70,000 resistors, 10,000 capacitors, 1,500 relays, and 6,000 manual switches, was a monument of engineering -- and an energy hog. The city of Philadelphia reportedly experienced brown-outs when ENIAC drew power at its home at the Moore School of Electrical Engingeering at the University of Pennsylvania.

ENIAC was a product of World War II. The military needed to develop firing tables for its artillery, so that gunners in the field could quickly look up which settings to use with a particular weapon on a particular target under particular conditions. The equations to determine these figures were so complex, they took days for a human to calculate; existing mechanical calculators could do slightly better. The Ballistics Research Laboratory (BRL), responsible for providing these figures to soldiers in the field, was falling behind. But BRL heard about the work of John Mauchly at the Moore School. In 1942, he had suggested using vacuum tubes to speed computer calculations.

Lieutenant Herman Goldstine of the BRL followed up on this. Soon BRL commissioned work on a new high-speed computer with Mauchly as chief consultant, his colleague J. Presper Eckert as chief engineer, and Goldstine as liaison. This was in 1943. It took about a year to design ENIAC, and 18 months to build it. By the time it was completed, in November 1945, the war had been over for three months. The project was 200 percent over budget (total cost approximately $500,000). But it had achieved what it set out to do. A calulation like finding the cube root of 2589 to the 16th power could be done in a fraction of a second. In a whole second ENIAC could execute 5,000 additions, 357 multiplications, and 38 divisions. This was up to a thousand times faster than its predecessors. A little too late for World War II, ENIAC was kept busy through the Cold War, working on such projects as calculations for the design of a hydrogen bomb.

ENIAC's main drawback was that programming it was a nightmare. In that sense it was not a general use computer. To change its program meant essentially rewiring it, with punchcards and switches in wiring plugboards. It could take a team two days to reprogram the machine.

Despite its flaws, the lessons learned from ENIAC helped computer developers improve the next generation, including EDVAC, UNIVAC, and Whirlwind, all of which improved upon programmability and memory storage. One of ENIAC's greatest feats was in showing the potential of what could be done.

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