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Photo on the left courtesy of: “U.S. Army Photo”, from M. Weik, “The ENIAC Story”. Photo on right courtesy of: “U.S. Army Photo”, from the archives of the ARL Technical Library.
By the 1940s, the Moore School had become the center for the development of electronic computation during World War II in response to urgent military needs. During the national emergency, the school's differential analyzer - the most sophisticated computing instrument available for scientific use at the time-was in constant use working out ballistic tables, although it was originally used to study nonlinear and varying parameter differential equations. In fact, the Moore School became something of an extension of the Army's Ballistic Research Laboratory (BRL), replacing human beings with handheld calculators. A trajectory that could take up to 40 hours to calculate using a desktop calculator could be computed in 30 minutes or so on the differential analyzer.
The need to even further speed the calculation and improve the accuracy of the firing and bombing tables resulted in the unveiling, in February of 1946, of the Electronic Numerical Integrator and Computer (ENIAC), the world's first operational, general purpose, electronic digital computer. ENIAC had no moving mechanical parts associated with the high-speed computational aspects of the machine. In fact, the only mechanical elements in the final system were external to the calculator itself: an IBM card reader for input, a card punch for output, and the associated relays. All prior machines had relied on such parts to perform their calculations, thus limiting their compactness and reliability, as well as the speed with which operations were executed.
By today's standards, ENIAC was a monster with 18,000 vacuum tubes, but it was the prototype from which most other modern computers evolved. It could perform 5,000 additions or subtractions or 360 multiplications of two 10-digit decimal numbers in one second. Its impact on the generation of firing tables was obvious. A skilled person with a desk calculator could compute a 60-second trajectory in about 20 hours. The Bush differential analyzer at the Moore School could produce the same result in 15 minutes, but the ENIAC required only 30 seconds.
However, ENIAC had one critical shortcoming: the lack of internally stored program capability. The Moore School researchers began developing preliminary designs for the Electronic Discrete Variable Computer (EDVAC). Around 1944, one of the most innovative scientists of the 20th century, John L. von Neumann, became a frequent visitor to the Moore School and eagerly joined discussions about the new and improved machine that would store its "instructions" in an internal memory system. In June 1945, he produced the first draft of a report on the EDVAC, recognized today as a seminal document in computer history.
Disputes over patent rights, among other issues, eventually led to von Neumann's disassociation with EDVAC's development team, but he nevertheless was on hand for the 1946 lecture series, entitled "Theory and Techniques for the Design of Electronic Digital Computers". The Moore School lectures featured talks by some of the biggest names in the field. Officially, 28 people from both sides of the Atlantic attended, but many others attended at least one lecture. Most expected the sessions to focus on ENIAC, but many speakers discussed designs and concepts for EDVAC. Together with von Neumann's paper, the Moore School lectures circulated enough information about EDVAC that its design became the basis for several later machines.
Meanwhile, in 1948, ENIAC was reassembled and converted into an internally stored-fixed program computer through the use of converter code. Many other improvements were made in ensuing years, including an independent motor-electricity generator set to provide steady, reliable power, a high-speed electronic shifter, and a 100-word static magnetic core memory developed by Burroughs Corporation. Until it was retired in 1955, ENIAC ran successfully for a total of 80,223 hours of operation. In addition to ballistics, applications included weather prediction, atomic energy calculations, cosmic ray studies, thermal ignition, random number studies, and wind tunnel design.
While ENIAC as built was never copied, and its influence on the logic and circuitry of succeeding machines is minimal, its development and the interactions among people associated with it critically impacted future generations of computers.
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