ENIAC (Electronic Numerical Integrator And Computer), the first large-scale, general purpose, digital computer. ENIAC was initially built for the United States military to calculate the paths of artillery shells. It was later used to make calculations for nuclear weapons research, weather prediction, and wind tunnel design. ENIAC was introduced to the public in February 1946 and was used until October 1955.

ENIAC was built by American physicist John W. Mauchly and American electrical engineer John Presper Eckert, Jr., at the Moore School of Electrical Engineering, University of Pennsylvania. Eckert and Mauchly successfully demonstrated ENIAC less than three years after the Army commissioned its construction. In 1947 ENIAC was moved from the University of Pennsylvania to its permanent home at the Aberdeen Proving Ground in Maryland. Only one system of its type was ever built, but it operated continuously until October 1955.

Unlike modern computers, which use microprocessors composed of thousands or millions of transistors, ENIAC used vacuum tubes to process data. It had about 18,000 tubes, each the size of a small light bulb. The computer was composed of 30 separate units with additional power supplies and cooling units. It weighed more than 30 tons, occupied 1800 sq ft and consumed 175 kw of power.

ENIAC contained 20 special storage registers called accumulators that stored intermediate and final calculations. Each accumulator held a ten-digit number. ENIAC used decimal arithmetic in its operations rather than the binary arithmetic common in today’s computers (see Number Systems). ENIAC could perform about 5000 calculations per second—more than 10,000 times slower than modern personal computers. It took ENIAC about 20 seconds to solve problems that had taken one or two days to complete manually. Initially, scientists programmed and entered data into ENIAC by manually setting switches and rewiring the machine. Later, a more efficient IBM punch-card reading machine was used to input data, while another IBM punch-card machine was used to store data. When ENIAC completed a calculation, it would notify operators by turning on a sequence of lights or punching certain sequences of cards.

ENIAC was designed to calculate continuously, day and night. However, because its circuitry was composed of a vast number of vacuum tubes that tended to burn out, ENIAC had to be constantly serviced. This continual servicing considerably reduced ENIAC’s net operating time. During a typical week, ENIAC was down for maintenance about one-third of the time. As soon as they completed the ENIAC design, Eckert and Mauchly signed a contract to build a successor, which they called EDVAC for Electronic Discrete Variable Automatic Computer. This more efficient design reduced the number of vacuum tubes in the EDVAC to about 4000.

Although it was the first large-scale machine to do routine calculations in a production environment, the ENIAC was not the first electronic computer. Between 1939 and 1942, John Atanasoff, a physics and mathematics professor at Iowa State University, and his graduate student Clifford Berry, assembled the Atanasoff-Berry Computer, which incorporated many digital circuit design innovations. Their system used the binary arithmetic system of 1s and 0s commonly used in today’s computers as well as a memory drum that stored data in a method similar to the storage technique used in modern memory chips.

After Eckert and Mauchly were granted a patent for the ENIAC, a long court battle began over who actually created the first modern electronic computer. Finally, in 1973, a federal judge invalidated the ENIAC patent and awarded recognition to Atanasoff and Berry, more than 30 years after their pioneering accomplishments.