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The ENIAC filled an entire room. With its bank of blinking lights and 6,000 manual switches, it looked like something we'd associate with a 1950s science fiction movie. Probably because it's what spawned those movies anyway. ENIAC, the mammoth machine credited with helping to start the computer age, fueled the public's imagination about how science and computers could revolutionize the world. Little did they realize how different that early computer was from the ones that would be built a mere fifty years later.
ENIAC stands for Electronic Numerical Integrator and Computer. John Mauchly and J. Presper Eckert built the machine at the University of Pennsylvania at the behest of the U.S. military. Mauchly had attracted the army's attention when he announced in 1942 that he thought vacuum tubes could be used to speed up the mechanical calculators being used at the time. Speedy calculations was just what the military needed during World War II as they pounded out tables for their weapons arsenal -- tables that could tell a soldier just which settings a particular piece of artillery needed under a particular set of conditions. The calculations involved could take a human days to complete.
By the time ENIAC was completed in November of 1945, the war was over. But ENIAC could do what it was supposed to. Filling up a 30 X 50 foot room, ENIAC was made of 17, 468 vacuum tubes, 70,000 resistors, and 10,000 capacitors -- not to mention all those lights and switches. Most importantly, the metal giant could add 5,000 umbers in a single second. That's not much by today's standards, but it was a thousand times faster than the mechanical calculators everyone had been using.
Unlike your modern desktop, ENIAC couldn't store any programming commands in its memory. It could only do one kind of program at a time, and to change the program meant completely rewiring it. Sometimes it could take a team of scientists two days to reprogram the machine.