ENIAC (pronounced ), short for Electronic Numerical Integrator And Computer , was the first general-purpose electronic computer. It was a Turing-complete, digital computer capable of being reprogrammed to solve a full range of computing problems. ENIAC was designed to calculate artillery firing tables for the U.S. Army's Ballistic Research Laboratory, but its first use was in calculations for the hydrogen bomb.
When ENIAC was announced in 1946 it was heralded in the press as a "Giant Brain". It boasted speeds one thousand times faster than electro-mechanical machines, a leap in computing power that no single machine has since matched. This mathematical power, coupled with general-purpose programmability, excited scientists and industrialists. The inventors promoted the spread of these new ideas by teaching a series of lectures on computer architecture.
The ENIAC's design and construction were financed by the United States Army during World War II. The construction contract was signed on June 5, 1943, and work on the computer was begun in secret by the University of Pennsylvania's Moore School of Electrical Engineering starting the following month under the code name "Project PX". The completed machine was unveiled on February 14, 1946 at the University of Pennsylvania, having cost almost $500,000 (nearly $6m in 2008, adjusted for inflation). It was formally accepted by the U.S. Army Ordnance Corps in July 1946. ENIAC was shut down on November 9, 1946 for a refurbishment and a memory upgrade, and was transferred to Aberdeen Proving Ground, Maryland in 1947. There, on July 29, 1947, it was turned on and was in continuous operation until 11:45 p.m. on October 2, 1955.
ENIAC was conceived and designed by John Mauchly and J. Presper Eckert of the University of Pennsylvania. The team of design engineers assisting the development included Robert F. Shaw (function tables), Chuan Chu (divider/square-rooter), Thomas Kite Sharpless (master programmer), Arthur Burks (multiplier), Harry Huskey (reader/printer), Jack Davis (accumulators) and Iredell Eachus Jr.
Description
The ENIAC was a modular computer, composed of individual panels to perform different functions. Twenty of these modules were accumulators, which could not only add and subtract but hold a ten-digit decimal number in memory. Numbers were passed between these units across a number of general-purpose buses, or trays, as they were called. In order to achieve its high speed, the panels had to send and receive numbers, compute, save the answer, and trigger the next operation—all without any moving parts. Key to its versatility was the ability to branch; it could trigger different operations that depended on the sign of a computed result.
Besides its speed, the most remarkable thing about ENIAC was its size and complexity. ENIAC contained 17,468 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors and around 5 million hand-soldered joints. It weighed 30 short tons (27 t), was roughly 8.5 by 3 by 80 feet (2.6 m × 0.9 m × 26 m), took up 680 square feet (63 m 2 ), and consumed 150 kW of power. Input was possible from an IBM card reader, and an IBM card punch was used for output. These cards could be used to produce printed output offline using an IBM accounting machine, an example of which would be the IBM 405.
ENIAC used ten-position ring counters to store digits; each digit used 36 vacuum tubes, 10 of which were the dual triodes making up the flip-flops of the ring counter. Arithmetic was performed by "counting" pulses with the ring counters and generating carry pulses if the counter "wrapped around", the idea being to emulate in electronics the operation of the digit wheels of a mechanical adding machine. ENIAC had twenty ten-digit signed accumulators which used ten's complement representation and could perform 5,000 simple addition or subtraction operations between any of them and a source ( e.g. , another accumulator, or a constant transmitter) every second. It was possible to connect several accumulators to run simultaneously, so the peak speed of operation was potentially much higher due to parallel operation.
It was possible to wire the carry of one accumulator into another accumulator to perform double precision arithmetic, but the accumulator carry circuit timing prevented the wiring of three or more for higher precision. The ENIAC used four of the accumulators, controlled by a special Multiplier unit, to perform up to 385 multiplication operations per second. The ENIAC also used five of the accumulators, controlled by a special Divider/Square-Rooter unit, to perform up to forty division operations per second or three square root operations per second.
The other nine units in ENIAC were the Initiating Unit (which started and stopped the machine), the Cycling Unit (used for synchronizing the other units), the Master Programmer (which controlled 'loop' sequencing), the Reader (which controlled an IBM punch card reader), the Printer (which controlled an IBM punch card punch), the Constant Transmitter , and three Function Tables .
The references by Rojas and Hashagen or (Wilkes 1956) give more details about the times for operations, which differ somewhat from those stated above. The basic machine cycle was 200 microseconds (20 cycles of the 100 kHz clock in the cycling unit), or 5,000 cycles per second for operations on the 10-digit numbers. In one of these cycles, ENIAC could write a number to a register, read a number from a register, or add/subtract two numbers. A multiplication of a 10-digit number by a d -digit number (for d up to 10) took d +4 cycles, so a 10- by 10-digit multiplication took 14 cycles, or 2800 microseconds—a rate of 357 per second. If one of the numbers had fewer than 10 digits, the operation was faster. Division and square roots took 13( d +1) cycles, where d is the number of digits in the result (quotient or square root). So a division or square root took up to 143 cycles, or 28,600 microseconds—a rate of 35 per second. (Wilkes 1956:20 states that a division with a 10 digit quotient required 6 milliseconds.) If the result had fewer than ten digits, it was obtained faster.
Reliability
ENIAC used common octal-base radio tubes of the day; the decimal accumulators were made of 6SN7 flip-flops, while 6L7s, 6SJ7s, 6SA7s and 6AC7s were used in logic functions. Numerous 6L6s and 6V6s served as line drivers to drive pulses through cables between rack assemblies.
Some electronics experts predicted that tube failures would occur so frequently that the machine would never be useful. This prediction turned out to be partially correct: several tubes burned out almost every day, leaving it nonfunctional about half the time. Special high-reliability tubes were not available until 1948. Most of these failures, however, occurred during the warm-up and cool-down periods, when the tube heaters and cathodes were under the most thermal stress. By the simple (if expensive) expedient of never turning the machine off, the engineers reduced ENIAC's tube failures to the more acceptable rate of one tube every two days. According to a 1989 interview with Eckert the continuously failing tubes story was therefore mostly a myth: "We had a tube fail about every two days and we could locate the problem within 15 minutes." In 1954, the longest continuous period of operation without a failure was 116 hours (close to five days).
Programming
Although the Ballistic Research Laboratory was the sponsor of ENIAC, one year into this three year project John von Neumann, a mathematician working on the hydrogen bomb at Los Alamos, became aware of this computer. Los Alamos subsequently became so involved with ENIAC that the first test problem run was computations for the hydrogen bomb, not artillery tables. The input/output for this test was one million cards.
The ENIAC could be programmed to perform complex sequences of operations, which could include loops, branches, and subroutines. The task of taking a problem and mapping it onto the machine was quite complex, and usually took weeks. After the program was figured out on paper, the process of getting the program "into" the ENIAC by manipulating its switches and cables took additional days. This was followed by a period of verification and debugging, aided by the ability to "single step" the machine.
The six women who did most of the programming of ENIAC were inducted in 1997 into the Women in Technology International Hall of Fame. As they were called by each other in 1946, they were Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman. Jennifer S. Light's essay, "When Computers Were Women" documents and describes the role of the women of ENIAC as well as outlines the historical omission or downplay of women's roles in computer science history.
ENIAC was a one-of-a-kind design and was never repeated. The freeze on design in 1943 meant that the computer design would lack some innovations that so
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