The Electronic Numerical Integrator and Computer (ENIAC ) was the first purely electronic general-purpose computer. He served the U.S. Army to calculate ballistic tables.


On behalf of the U.S. Army, he was from 1942 by J. Presper Eckert and John W. Mauchly developed at the University of Pennsylvania and presented to the public on February 14, 1946.

Mauchly and Eckert founded in 1946 a computer company, the Eckert - Mauchly Computer Corporation, which was later acquired by Remington Rand. 1947, a patent was filed, the validity of which began in 1967 years of court proceedings. They meant that the patent was declared in 1973 because of the Atanasoff -Berry already from computer ( ABC) known properties for invalid; because Mauchly during a visit to Atanasoff in 1941 had the opportunity to study the ABC, and probably drew some inspiration from it, the ENIAC was considered by the court as a derivative work. The credit for the invention of the first electronic computer, the Mauchly and Eckert had shared until then, has since been transferred to Atanasoff.

From Philadelphia from the ENIAC in 1947 moved to the nearby Aberdeen Ballistic Research Lab. ENIAC was shut down on October 2, 1955.


Similarly, the Atanasoff -Berry Computer (1938-1942) and the British Colossus ( 1943), a cryptographic special-purpose computer, the ENIAC used vacuum tubes for the representation of numbers and their electrical pulses for transmission. This resulted in a far greater computing power than that of Konrad Zuse's Z3 ( 1941), although a more modern architecture had, but still based on electromechanical relays. As the ASCC (built in 1939-1944, and later as "Mark I" known) used the ENIAC a decimal system to represent numbers.

The ENIAC consisted of 40 operating in parallel components, each of which was 60 cm wide, 270 cm high and 70 cm deep. The entire system was built in a U shape, claimed an area of ​​10 m × 17 m and weighed 27 tons. It consisted of 17,468 vacuum tubes, 7,200 diodes, 1,500 relays, 70,000 resistors and 10,000 capacitors. The power was 174 kW. The construction of the ENIAC cost $ 468,000 - an amount that was available only because of the high demand for computing power on the part of the U.S. Army (equivalent to a present value of approximately U.S. $ 6,950,000 ). Compared to its predecessors the ENIAC already impressed by its sheer size.

A major problem in the development of the ENIAC was the error rate of electron tubes. If only one of the 17,468 tubes failed, the entire machine figured wrong. To keep the cost of these inevitable losses to a minimum, especially diagnostic programs were built into the ENIAC, which facilitated the discovery of a tube to be replaced. A countermeasure was to incorporate more tubes than you would have actually needed, and this can only be operated with about 10 % of their rated capacity. It was also noticed that more tubes when switching on and off were broken as during operation. As a consequence, we went over to the ENIAC simply no longer off. The downtime could be reduced to a few hours per week.


An addition / subtraction took 0.2 milliseconds, a multiplication of up to 2.8 ms, a division up to 24 ms and a square root of more than 300 ms.

Operation of the ENIAC

Basic component for the function of the ENIAC was the battery, which could store as well as adding a 10-digit signed decimal and subtract. Each of the 20 accumulators could perform such a computation operation in 0.2 milliseconds. This time interval is referred to as addition cycle. For calculations with double precision two accumulators could interconnect.

More arithmetic components were the multiplier ( three copies) and the Divider / Square - Rooter. A multiplier implemented a multiplication table, after a subroutine was controlled, ran on four accumulators. Multiplication lasted ( depending on the length of the numbers ) up to 2.8 milliseconds. Similarly, the Divider / Square - Rooter was constructed, the space required for a division or square root up to 65 milliseconds (13 addition cycles per digit). The programming of complex calculations was the Master Programmer (two copies) possible, the recursive programming allowed.

The Initiating Unit was responsible for the start of the installation. When the ENIAC took the flip-flops to random values, so the components were in an undefined state. A special program of the Initiating Unit, flip-flops were brought into a defined state, eg, the accumulators are initialized to 0. Furthermore, the Initiating Unit had a start button with the ENIAC, a program was started manually. As the clock Cycling Unit, which provided the other components via static cable with control pulses served. She could also be connected in a step -by-step mode, the simplified troubleshooting.

Data entry

The ENIAC was programmed by connecting the individual components with cables and the required operations ceased on rotary switches. The ENIAC was programmed by women, the " ENIAC women ": Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Frances Bilas and Ruth Teitelbaum. They had previously employed for the military ballistic calculations on mechanical desk calculators.

The components of the ENIAC were statically connected with each other to receive the clock pulses of the cycling unit. More static connections existed among the cooperating components (eg between a multiplier and the 4 associated accumulators). All other connections for the execution of a program had to be inserted manually. For the transmission of program pulses were at base height horizontally extending cables in trays Program, for the number of pulses were Digit trays used at head level. On trays and components were jacks could be inserted into the cable.

A significant disadvantage of the architectural ENIAC was the lack of instruction memory. Even the Z3 and Mark I read their instructions from a punched tape, while the ENIAC had to be rewired for each program. Following ideas of John von Neumann of the ENIAC in 1948 was converted to a computer with instruction memory. This slowed its computing power to 1 /6, but the duration of reprogramming also decreased, so that a total of one time gain was achieved.

Data output

As a read-only memory of the Constant Transmitter served (consisting of three components) and the Function Tables ( three components, each with three copies). The former was mainly used for controlling a punch card reader. In the latter (only six digits individually adjustable however ) were stored in an access time of addition of five cycles per 104 ten-digit decimal numbers. Calculation results could also be printed: About the Printer Panel (consisting of three components) was a hole card printer can be controlled.

An immediate visual output was integrated into the accumulators: In the upper area of ​​the component, there were 102 glow lamps to display the currently stored number (ten each for each of the ten digits, two for the sign ).

Cultural impact

On the occasion of the first public presentation of the ENIAC in February 1946 inside out to a halved ping-pong ball over each lamp - a design that is a model for many subsequent computer was and downright influential for those science fiction.

Comparison with other early computers