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With help from grad student Clifford Berry and a few research grants, Atanasoff built a prototype of the ABC computer, which was demonstrated in October 1939. A more advanced version, which contained 300 tubes and took several seconds to complete a math problem, was erected in 1941. It worked, but the outbreak of war forced both Atanasoff and Berry to drop it and move to more urgent defense projects.
Hear ENIAC programmer Jean Bartik describe the mammoth computer.
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Mauchly, then a professor of physics at Ursinius College, was working on an entirely different kind of science, researching ways to better predict weather with an analog device called a harmonic analyzer. Atanasoff attended a lecture by Mauchly in December 1940 and afterward the two began to correspond and discuss potential for electronic computers.
Mauchly soon had another life-changing encounter. Obsessed with electronics, he enrolled in a course at the Moore School being taught by Eckert. By the end of 1941, Mauchly was teaching at Penn and discussing computing ideas with Eckert.
The two had complementary skills. Mauchly was an expert in physics and math, but early in his career had disdained engineering. Eckert, the only son from a wealthy, globe-trotting Philadelphia family, was a natural tinkerer. At age 14, he rigged up an intercom system in his dad's building, and the Connecticut Telephone and Telegraph later bought it from him.
"Eckert was an absolute genius as an electrical engineer. He was one of the best designers of the 20th century," said Michael Williams, professor emeritus of history at University of Calgary and president-elect of The Institute of Electrical and Electronics Engineers. Mauchly, he added, was able to envision how such a machine might work.
Ideas on paper come to life
Mauchly exhibited that vision in a five-page memo titled "The Use of Vacuum Tube Devices in Calculating." It presented ideas that wove their way through the university-government bureaucracy and ultimately resulted in contract W-670-ORD-4926. Under that agreement, signed June 5, 1943, Penn would research the possibility of an electronic differential analyzer for the U.S. Army Ordnance Department.
The proposed work was to last six months and cost $61,700--a vast underestimation, it would turn out, of both time and money. ENIAC wouldn't be tested internally for two and a half years, in November 1945, at a final cost of $487,000. Despite the overruns, however, it was an engineering marvel.
At the heart of ENIAC was a device called a ring counter, which consisted of 10 vacuum tubes in a circle. A "5" would be represented by a pulse at the fifth tube. If a person added 9 to that, the pulse would shift to the fourth tube, while the first tube on a second ring--representing the 10--would receive a pulse.
Ten ring counters were placed in each accumulator, which could store numbers ranging up to 10 billion minus one (9,999,999,999) or down to negative 10 billion plus one. When a single accumulator hit its maximum, a pulse could be sent via wire to a second one, continuing the process. In all, ENIAC contained 20 accumulators spread over 40 racks networked together through plug boards. Data was stored in pulses in 5-foot mercury tubes.
Six technicians were largely responsible for working the mathematical equations and programming functions. Because these jobs were considered an extension of clerical work, they were filled by women, as was the practice of the day.
"They were the first programmers and they didn't get the credit they deserved," said Kathryn Kleiman, an internet privacy lawyer with McLeod, Watkinson and Miller and a member of the Association for Computing Machinery's committee on women in computing.
One of the biggest challenges was preventing vacuum tubes from blowing out. Because the tubes would be required to pulse 100,000 times a second and the machine had so many of them, the threat of a blowout was constant. Eckert solved the problem by running below their threshold and designing the system to operate under the "worst worst scenarios," Williams said.
The scientists faced another concern that was decidedly low-tech but equally important: rodent control. "We knew mice would eat the insulation off the wires, so we got samples of all the wires that were available in a cage with a bunch of mice to see which insulation they did not like. We used that wire," Eckert said in a 1989 interview with Alex Randall, professor of electrical engineering at the University of the Virgin Islands and friend of the Eckert family.
Finally, ENIAC underwent its first full test in November 1945, when computational problems from the H-bomb product were fed into it. On Feb. 14, 1946, the Moore School invited Army officials, Penn professors and select scientists from around the country for a demonstration. Contrary to popular myth, the lights in Philadelphia did not dim and soldiers did not salute the machine.
Also contrary to popular myth, most people didn't care. Although the Moore school immediately began to get inquiries from other universities and researchers, the public mostly ignored it, despite front-page news articles. That, of course, would change with time.
"I don't think one could say there was much fanfare just after the unveiling," wrote Arthur Burks, one of the original engineers. "Those in the know had great expectations, but even these (expectations) would not have even approached what actually occurred over the years."
See footage of the ENIAC's creators with their computing machine in action, bright lights, vacuum tubes and all.
"I was already wearing a plastic pocket protector and thick black glasses--taped together--so I didn't need something to increase my social dysfunction."
"I bought my first computer when I was 15 in 1980. It was an Apple II, which back then was the most popular PC in the U.S."
"I still had to re-key them everytime I wanted to change programs, but this wasn't too bad as the TI-58 only had enough memory for about 240 instructions."
See the men, women, and metal behind the making of the ENIAC.
Editors: Kari Dean McCarthy; Mike Yamamoto
Production: Bernie McGinn; Jennifer Guevin; Vincent Tremblay
Design: Ellen Ng