The History of the ENIAC Computer

John Mauchly and John Presper Eckert

Glen Beck (background) and Betty Snyder (foreground) program ENIAC in BRL building 328. Public Domain

"With the advent of everyday use of elaborate calculations, speed has become paramount to such a high degree that there is no machine on the market today capable of satisfying the full demand of modern computational methods." - Excerpt from the ENIAC patent (U.S.#3,120,606) filed on June 26, 1947.


In 1946, John Mauchly and John Presper Eckert developed the ENIAC I or Electrical Numerical Integrator And Calculator. The American military sponsored their research because they needed a computer for calculating artillery-firing tables, the settings used for different weapons under varied conditions for target accuracy.

The Ballistics Research Laboratory or BRL is the branch of the military responsible for calculating the tables and they became interested after hearing about Mauchly's research at the University of Pennsylvania's Moore School of Electrical Engineering. Mauchly had previously created several calculating machines and had begun in 1942 designing a better calculating machine based on the work of John Atanasoff, an inventor who used vacuum tubes to speed up calculations.

Partnership of John Mauchly & John Presper Eckert

On May 31, 1943, the military commission on the new computer began with Mauchly serving as the chief consultant and Eckert as the chief engineer. Eckert had been a graduate student studying at the Moore School when he and Mauchly met in 1943. It took the team about one year to design the ENIAC and then 18 months plus 500,000 tax dollars to build it. And by that time, the war was over. The ENIAC was still put to work though by the military, performing calculations for the design of a hydrogen bomb, weather prediction, cosmic-ray studies, thermal ignition, random-number studies and wind-tunnel design.

What Was Inside The ENIAC?

The ENIAC was a complex and elaborate piece of technology for the time. It contained 17,468 vacuum tubes along with 70,000 resistors, 10,000 capacitors, 1,500 relays, 6,000 manual switches and 5 million soldered joints. Its dimensions covered 1,800 square feet (167 square meters) of floor space, weighed 30 tons and running it consumed 160 kilowatts of electrical power. There was even a rumor that once turned on the machine caused the city of Philadelphia to experience brownouts. However, the rumor was first reported incorrectly by the Philadelphia Bulletin in 1946 and since then has been regarded as an urban myth.

In just one second, the ENIAC (one thousand times faster than any other calculating machine to date) could perform 5,000 additions, 357 multiplications or 38 divisions. The use of vacuum tubes instead of switches and relays resulted in the increase in speed, but it was not a quick machine to re-program. Programming changes would take the technicians weeks and the machine always required long hours of maintenance. As a side note, research on the ENIAC led to many improvements in the vacuum tube.

Contributions of Doctor John Von Neumann

In 1948, Doctor John Von Neumann made several modifications to the ENIAC. The ENIAC had performed arithmetic and transfer operations concurrently, which caused programming difficulties. Von Neumann suggested that switches can be used to control code selection so that pluggable cable connections could remain fixed. He added a converter code to enable serial operation.

Eckert-Mauchly Computer Corporation

In 1946, Eckert and Mauchly started the Eckert-Mauchly Computer Corporation. In 1949, their company launched the BINAC (BINary Automatic) computer that used magnetic tape to store data.

In 1950, the Remington Rand Corporation bought the Eckert-Mauchly Computer Corporation and changed the name to the Univac Division of Remington Rand. Their research resulted in the UNIVAC (UNIVersal Automatic Computer), an important forerunner to today's computers.

In 1955, Remington Rand merged with the Sperry Corporation and formed Sperry-Rand. Eckert remained with the company as an executive and continued with the company when it later merged with the Burroughs Corporation to become Unisys. Eckert and Mauchly both received the IEEE Computer Society Pioneer Award in 1980.

On October 2, 1955 at 11:45 p.m., with the power finally shut off, the ENIAC was retired.