The ENIAC (short for electronics Numerical integrator and computer) was the first electronic digital multipurpose computer and one of the first computers at all. On behalf the US army it was developed starting from 1942 by J. Presper Eckert and John W. Mauchly at the university by Pennsylvania and introduced on 14 February 1946 of the public. Up to its disconnection on 2 October 1955 it served the US army for the computation of ballistic tables.

Similarly the Atanasoff Berry computer (1938-1942) and the British Colossus (1943), a cryptographic special-purpose computer, the ENIAC used electron tubes for the representation of numbers and electrical pulses for their transmission. This caused a clearly higher arithmetic performance than of Konrad the Zuses Z3 (1941), which exhibited a comparatively modern architecture, but still on mechanical relays was based. Like the ASCC (builds 1939 and 1944 between, also admits as Mark I) the ENIAC used a decimal system for the representation of numbers.

The ENIAC consisted of 40 parallel working components, of which each 60cm was deep broad, 270cm highly and 70cm. The complete plant was developed in U-form, stressed a surface of 10x17m and weighed 27t. The current consumption of the 17,468 electron tubes, 7,200 diodes, 1,500 relays, 70,000 resistances and 10,000 condensers was with 174kW. The building of the ENIAC cost 468,000$, an amount, which only due to the high need of arithmetic performance on the part of the US army for the order. Compared with its predecessors the ENIAC already impresses by its almost size.

The ENIAC could add, subtracts, multiplies, divides and square roots to draw. He was programmed, by connecting the individual components with cables and stopping the desired operations on rotary switches. An addition/a subtraction needed 0.2 milliseconds, a multiplication up to 2,8 ms, a division up to 24 ms and a square root more than 300 ms. The ENIAC was programmed at the beginning of only by women, "„ENIAC girls "“, usually studied mathematician inside. They had before accomplished ballistic computations at mechanical desk calculators at the homeland front. A large problem with the development of the ENIAC was the fault liability of the electron tubes. If only one of the 17,468 tubes failed, the entire machine counted incorrectly. In order to keep the costs of these inevitable losses small, into the ENIAC particularly diagnostic programs were built, which facilitated a finding of a tube which can be exchanged. In addition it was noticed that when switching on and off broken went to more tubes, as during the current enterprise. As consequence one turned into not to switch the ENIAC off simply any longer. The down-time could be reduced in such a way on only few hours for each week, according to the circumstances outstanding result.

As test run before its completion end 1945 computations were accomplished briefly in the context of the development of the hydrogen bomb. This was however an exception. From Philadelphia the ENIAC moved 1947 in the nearby Ballistic Research lab in Aberdeen and computed up to its disconnection projectile courses.

Mauchly and Eckert created 1946 a computer company, which was taken over later by Remington edge. The ENIAC was announced 1947 to the patent. In the year 1967 it came to a court controversy of many years over the validity of the patent. 1973 were finally explained it for invalid, since already Atanasoffs ABC exhibited some characteristics, which were patented for the ENIAC. Since Mauchly had opportunity during an attendance with Atanasoff in the year 1941 to study the ABC and probably some, was regarded the ENIAC drew inspiration from it work derived from the court as. The fame for the invention of the first electronic computer, which Mauchly and Eckert had up to then divided, since that time turns into on Atanasoff.

Nontheless the building of the ENIAC was perhaps a gloss achievement and the largest step in the development of the computer, which was ever made.

Function mode of the ENIAC

Fundamental component for the function of the ENIAC was the accumulator, as well as which stores a signed decimal number with 10 digits to add and could subtract. Each of the 20 accumulators could accomplish such an arithmetic operation in 0.2 milliseconds. This time interval is called also addition cycle. For calculations with double accuracy two accumulators could be connected.

Further arithmetic components were the multiplicator (3 copies) and the Divider/Square Rooter. A multiplicator implemented a multiplication table, according to which a subroutine was steered, which ran on 4 accumulators. A multiplication lasted (depending upon length of the numbers) up to 2.8 milliseconds. Similarly also the Divider/Square Rooter was designed, which for a division and/or square root needed up to 65 milliseconds (13 addition cycles for each number). The programming of complex computations was possible for recursive programming with the master Programmer (2 copies), permitted.

For the start of the plant the Initiating unit was responsible. When switching on of the ENIAC on the flip-flops took coincidental values, so that the components were in an undefined condition. By a special program the flip-flops could be brought to the Initiating unit into a defined condition, and be e.g. initialized the accumulators with 0. The moreover one the Initiating unit had an activate button, with which a ENIAC program was started manually. As master clock the Cycling served unit , the other components via static cables with tax pulses supplied. It could be switched also into a step for step mode, the error tracing simplified.

As ROM the Constant transmitters (consisting of 3 components) and the Function Tables (3 components, ever 3 copies) served. First served mainly for the control of a punch card reader. On the latters 104 ten-digit decimal numbers each (however only 6 places individually adjustable) were stored with an access time by 5 addition cycles. Results of computation could be also printed: Over the printer panel (consisting of 3 components) could be headed for a punch card printer.

A direct visual expenditure was integrated into the accumulators: Within the upper range of the component there were 102 Neonbirnchen for the announcement of the up-to-date stored number (ever 10 for everyone of the 10 numbers, 2 for the sign). On the occasion of the first public presentation of the ENIAC in February 1946 one inverted a halved Tischtennisball over each light - a Design, the model for many following computers almost was and style-forming for the Science Fiction at that time.

The components of the ENIAC were statically connected, in order to receive the clock pulses of the Cycling unit. There were further static connections between the co-operating components (e.g. between a multiplicator and the 4 assigned accumulators). All further connections for the expiration of a program had to be put manually. For the transmission of program pulses there was running cable in Program Trays, for number pulses on foot height horizontally the digit Trays in addendum was used. At Trays and components there were sockets, into which cables could be put.

A clear architectural disadvantage of the ENIAC was the absence of an instruction memory. Already the Z3 and the Marks of I read its instructions of a magnetic tape, while the ENIAC for each program had again to be verkabelt. After ideas John von Neumanns was converted the ENIAC 1948 to a computer with instruction memory. This slowed down its arithmetic performance on 1/6, but the duration of reprogramming was reduced likewise, so that altogether a time gained was obtained.

References

• J.P. Eckert Jr., J.W. Mauchly, H.H. Goldstine, J.G. Brainerd: Description OF the ENIAC and COMMENT on electronics digitally Computing Machines. Moorlands School OF Electrical engineering, University OF Pennsylvania, 1945.
• H.H. Goldstine, A. Goldstine (1946): The electronics Numerical integrator and computer (ENIAC). In B. Randell (Eds.): The Origins OF digitally computer, Springer publishing house (1982).
• J. Van of the mirrors, J.F. rope, T.F. Ala'ilima, and L.P. Ang (2000). The ENIAC: History, operation and Reconstruction in VLSI. In R. Rojas (Eds.): The roofridge of computer; History and Architectures, WITH press.

Related links

• Archives for the history of the computer with many texts and pictures to the ENIAC (EN)
• Article over the emergence of the ENIAC (EN)
• Telepolis article over the ENIAC
• Facts to the ENIAC (EN)
• The ENIAC in the HNF computer museum
• The ENIAC Programmiererinnen
• Reproduction of the ENIAC on a chip (EN)
• ENIAC simulation (EN)

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