Saturday, October 17, 2009

Computing - Everything Is Change

On December 7, 1941, Japanese forces attacked the U.S. Navy base at Pearl Harbor. The U.S. was at war. Mobilization meant the army needed ever more fi ring tables, each of which contained about 3,000 entries. Even with the Differential Analyzer, the backlog of calculations at Aberdeen was mounting.

Eighty miles up the road from Aberdeen, the Moore School of Electrical Engineering at the University of Pennsylvania had its own differential analyzer. In the spring of 1942 a 35-yearold instructor at the school named John W.Mauchly had an idea for how to speed up calculations: construct an “electronic computor” [sic] that would use vacuum tubes in place of the mechanical components. Mauchly, a theoretically- minded individual, found his complement in an energetic young researcher at the school named J. Presper (“Pres”) Eckert, who had already shown sparks of engineering genius.

A year after Mauchly made his original proposal, following various accidental and bureaucratic delays, it found its way to Lieutenant Herman Goldstine, a 30-year-old Ph.D. in mathematics from the University of Chicago who was the technical liaison officer between Aberdeen and the Moore School. Within days Goldstine got the go-ahead for the project. Construction of the ENIAC—for Electronic Numerical Integrator and Computer—began on April 9, 1943. It was Eckert’s 23rd birthday.

Many engineers had serious doubts about whether the ENIAC would ever be successful. Conventional wisdom held that the life of a vacuum tube was about 3,000 hours, and the ENIAC’s initial design called for 5,000 tubes. At that failure rate, the machine would not function for more than a few minutes before a broken tube put it out of action. Eckert, however, understood that the tubes tended to fail under the stress of being turned on or off. He knew it was for that reason radio stations never turned off their transmission tubes. If tubes were operated significantly below their rated voltage, they would last longer still. (The total number of tubes would grow to 18,000 by the time the machine was complete.)

Eckert and his team completed the ENIAC in two and a half years. The finished machine was an engineering tour de force, a 30-ton behemoth that consumed 150 kilowatts of power. The machine could perform 5,000 additions per second and compute a trajectory in less time than a shell took to reach its target. It was also a prime example of the role that serendipity often plays in invention: although the Moore School was not then a leading computing research facility, it happened to be in the right location at the right time with the right people.

Yet the ENIAC was finished in 1945, too late to help in the war effort. It was also limited in its capabilities. It could store only up to 20 numbers at a time. Programming the machine took days and required manipulating a patchwork of cables that resembled the inside of a busy telephone exchange. Moreover, the ENIAC was designed to solve ordinary differential equations. Some challenges—notably, the calculations required for the Manhattan Project—required the solution of partial differential equations.

John von Neumann was a consultant to the Manhattan Project when he learned of the ENIAC on a visit to Aberdeen in the summer of 1944. Born in 1903 into a wealthy Hungarian banking family, von Neumann was a mathematical prodigy who tore through his education. By 23 he had become the youngest ever privatdozent (the approximate equivalent of an associate professor) at the University of Berlin. In 1930 he emigrated to the U.S., where he joined Albert Einstein and Kurt Gödel as one of first faculty members of the Institute for Advanced Study in Princeton, N.J. He became a naturalized U.S. citizen in 1937.

Von Neumann quickly recognized the power of electronic computation, and in the several months after his visit to Aberdeen, he joined in meetings with Eckert, Mauchly, Goldstine and Arthur Burks—another Moore School instructor— to hammer out the design of a successor machine, the Electronic Discrete Variable Automatic Computer, or EDVAC.

The EDVAC was a huge improvement over the ENIAC. Von Neumann introduced the ideas and nomenclature of Warren McCullough and Walter Pitts, neuroscientists who had developed a theory of the logical operations of the brain (this is where we get the term computer “memory”). Like von Neumann, McCullough and Pitts had been influenced by theoretical studies in the late 1930s by British mathematician Alan Turing, who established that a simple machine can be used to execute a huge variety of complex tasks. There was a collective shift in perception around this time from the computer as a mathematical instrument to a universal informationprocessing machine.

Von Neumann thought of the machine as having five core parts: Memory held not just numerical data but also the instructions for operation. An arithmetic unit performed calculations. An input “organ” enabled the transfer of programs and data into memory, and an output organ recorded the results of computation. Finally, a control unit coordinated operations. This layout, or architecture, makes it possible to change the computer’s program without altering the physical structure of the machine. Moreover, a program could manipulate its own instructions. This feature would not only enable von Neumann to solve his partial differential equations, it would confer a powerful fl exibility that forms the very heart of computer science.

In June 1945 von Neumann wrote his classic First Draft of a Report on the EDVAC on behalf of the group. In spite of its unfi nished status, it was rapidly circulated among the computing cognoscenti with two consequences. First, there never was a second draft. Second, von Neumann ended up with most of the credit.

Source of Information : Scientific American September 2009

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