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ENIAC, short for Electronic Numerical Integrator And Computer, was the first all-electronic computer designed to be Turing-complete, capable of being reprogrammed by rewiring to solve a full range of computing problems. It was preceded in 1941 by the fully tape-programmable but still mechanical Z3 designed by Konrad Zuse and by the all-electronic rewire to reprogram but not fully general purpose British Colossus computer. Both ENIAC and Colossus used thermionic valves, that is, vacuum tubes, while Z3 used mechanical relays. The requirement to rewire to reprogram ENIAC was removed in 1948.
ENIAC was developed and built by the U.S. Army for their Ballistics Research Laboratory with the purpose of calculating ballistic firing tables. ENIAC was conceived of and designed by J. Presper Eckert and John William Mauchly of the University of Pennsylvania. The computer was commissioned on May 17, 1943 as Project PX, constructed at the Moore School of Electrical Engineering from mid-1944, and formally operational from February 1946 having cost almost $500,000. It was then shut off on November 9, 1946 for a refurbishment and a memory upgrade. ENIAC was unveiled on February 14, 1946 at the University of Pennsylvania and was transferred to the Aberdeen Proving Grounds, Maryland in 1947. There, on July 29th of that year, it was turned on and would be in continuous operation until 1955.
ENIAC received a lot of press for its sheer size, but in some ways it was not the state-of-the-art of its era. Unlike Konrad Zuse's Z3 of 1941 and Howard Aiken's MARK I of 1944 it had to be rewired to run a new program (Z3 and MARK I read their programs off a tape). Furthermore, unlike Z3 and most modern computers, ENIAC's registers performed decimal arithmetic rather than binary.
ENIAC used ten-position ring counters to store digits. Arithmetic was performed by "counting" pulses with the ring counters and generating carry pulses if the counter "wrapped around", the idea being to emulate in electronics the operation of the digit wheels of a mechanical adding machine. Each of ENIAC's twenty ten-digit signed accumulators could perform 5,000 simple addition operations every second (total 100,000 addition operations per second). The ENIAC could only manage 357 multiplication operations per second or 38 division (or square root) operations per second.
Physically ENIAC was a monster—it contained 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors and around 5 million hand-soldered joints. It weighed 30 tons, was roughly 2.4 m by 0.9 m by 30.5 m, took up 167 mē and consumed 160 kW of power. Input was possible from an IBM card reader, while an IBM printer could produce printed output.
ENIAC used common octal-base radio tubes of the day; the decimal accumulators were made of 6SN7 flip-flops, while 6L7s, 6SJ7s, 6SA7s and 6AC7s were used in logic functions. Numerous 6L6s and 6V6s served as line drivers to drive pulses through cables between rack assemblies.
Some electronics experts predicted that tube failures would occur so frequently that the machine would never be useful. This prediction turned out to be partially correct: several tubes burned out almost every day, leaving it nonfunctional about half the time. Special high-reliability tubes were not available until 1948, so Eckert and Mauchly had to use commonplace tube types. Most of these failures, however, occurred during the warm-up and cool-down periods, when the tube heaters and cathodes were under the most thermal stress. By the simple (if expensive) expedient of never turning the machine off, the engineers reduced ENIAC's tube failures to the more acceptable rate of one tube every two days. In 1954, the longest continuous period of operation without a failure was 116 hours (close to five days). Given the technology available at the time, this failure rate was remarkably low, and stands as a tribute to the precise engineering of ENIAC.
Eckert and Mauchly took the experience they gained and founded the Eckert-Mauchly Computer Corporation, producing their first computer, BINAC, in 1949 before being acquired by Remington Rand in 1950 and renamed as their Univac division.
ENIAC ran until October 2, 1955. It was a one-off design and was never repeated. The freeze on design in 1943 meant that the computer had a number of short-comings which were not solved, notably the inability to store a program. But the ideas generated from the work and the impact it had on people such as John von Neumann were profoundly influential in the development of later computers, initially EDVAC, EDSAC and SEAC. A number of improvements were also made to ENIAC from 1948, including a primitive read-only stored programming mechanism [1] (http://ftp.arl.mil/~mike/comphist/48eniac-coding/) using the Function Tables as program ROM, an idea proposed by John von Neumann. This modification reduced the speed of ENIAC by a factor of 6 times, but as it also reduced the reprogramming time to hours instead of days, it was considered well worth the loss of performance.
As of 2004, a chip of silicon measuring 0.02 inches square holds the same capacity as the ENIAC, which occupied a large room.
References
- Scott McCartney (1999). ENIAC: The Triumphs and Tragedies of the World's First Computer. Walker & Co. ISBN 0802713483.
See also
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