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A scientist works inside of ENIAC

The year 1996 marked the fiftieth anniversary of the ENIAC computer, the first large-scale general-purpose electronic computer. Built at the University of Pennsylvania's Moore School of Electrical Engineering, ENIAC is an acronym for "Electronic Numerical Integrator and Computer," but its birth lay in World War II as a classified military project known only as Project PX. The ENIAC is important historically, because it laid the foundations for the modern electronic computing industry. More than any other machine, the ENIAC demonstrated that high-speed digital computing was possible using the then-available vacuum tube technology.

The ENIAC was a large-scale, general purpose digital electronic computer. Built out of some 17,468 electronic vacuum tubes, ENIAC was in its time the largest single electronic apparatus in the world. There were two fundamental technical innovations in the ENIAC. The first had to do with combining very diverse technical components and design ideas into a single system that could perform 5,000 additions and 300 multiplications per second. Although slow by today's standards--current microprocessors perform 100 million additions per second--this was two to three orders of magnitude (100 to 1,000 times) faster than existing mechanical computers or calculators. The sheer speed of the machine and its limited, but sufficiently versatile, programming mechanisms allowed the ENIAC to demonstrate that electronic computing could be applied to some of the nation's most pressing problems, such as the development of the hydrogen bomb. The significance of electronic computing to national security was an important factor in the birth of the modern computing industry.

click for larger imageThe ENIAC cost over $500,000 to make and was divided into thirty autonomous units, twenty of which were called accumulators. Each accumulator was essentially a high-speed ten-digit adding machine that could also store the results of its calculations. The ENIAC was a decimal machine, which meant that each of the ten digits in the accumulators counted from zero (0) through nine (9) using a particular configuration of electronic circuits known as a ring counter. To accelerate certain arithmetic operations the ENIAC also had a multiplier and divider-square rooter. The multiplier employed a resistor matrix to perform one-digit multiplications and was designed with additional control circuitry to multiply successive digits drawn from two accumulators holding the multiplier and multiplicand.

The ENIAC was controlled through a train of electronic pulses. Each unit of the ENIAC was capable of issuing a control pulse that would initiate computation in one or more of the other units. This meant that a "computer program" on the ENIAC consisted principally of manually wiring the different units of the machine so that they would perform their operations in the desired sequence. A typical program on the ENIAC thus consisted of a nest of wires interconnecting the various units of the machine. Special wiring trays gave some semblance of order to these wires, but programming the ENIAC was nevertheless a difficult affair.


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