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First electronic general purpose digital computer

ENIAC (/'//ɛ//n//i//æ//k///; Electronic Numerical Integrator and Computer) was the first programmable, electronic, general purpose digital computer, completed in 1945. Other computers had some of these features, but ENIAC was the first to have them all. It was Turing complete and able to solve "a large class of numerical problems" through reprogramming. ENIAC was designed by John Mauchly and J. Presper Eckert to calculate artillery firing tables for the United States Army's Ballistic Research Laboratory (which later became a part of the Army Research Laboratory). However, its first program was a study of the feasibility of the thermonuclear weapon. ENIAC was completed in 1945 and first put to work for practical purposes on December 10, 1945. ENIAC was formally dedicated at the University of Pennsylvania on February 15, 1946, having cost $487,000 (487000.0 in 1943 is equivalent to about <calculated amount> in recent years), and called a "Giant Brain" by the press. It had a speed on the order of one thousand times faster than that of electro mechanical machines. ENIAC was formally accepted by the U. S. Army Ordnance Corps in July 1946. It was transferred to Aberdeen Proving Ground in Aberdeen, Maryland in 1947, where it was in continuous operation until 1955.

ENIAC's design and construction was financed by the United States Army, Ordnance Corps, Research and Development Command, led by Major General Gladeon M. Barnes. The total cost was about $487,000, 487000.0 in 1943 is equivalent to about <calculated amount> in recent years. The construction contract was signed on June 5, 1943; work on the computer began in secret at the University of Pennsylvania's Moore School of Electrical Engineering the following month, under the code name "Project PX", with John Grist Brainerd as principal investigator. Herman H. Goldstine persuaded the Army to fund the project, which put him in charge to oversee it for them. ENIAC was designed by Ursinus College physics professor John Mauchly and J. Presper Eckert of the University of Pennsylvania, U. S. The team of design engineers assisting the development included Robert F. Shaw (function tables), Jeffrey Chuan Chu (divider/square rooter), Thomas Kite Sharpless (master programmer), Frank Mural (master programmer), Arthur Burks (multiplier), Harry Huskey (reader/printer) and Jack Davis (accumulators). Significant development work was undertaken by the female mathematicians who handled the bulk of the ENIAC programming: Jean Jennings, Marlyn Wescoff, Ruth Lichterman, Betty Snyder, Frances Bilas, and Kay McNulty. In 1946, the researchers resigned from the University of Pennsylvania and formed the Eckert–Mauchly Computer Corporation. ENIAC was a large, modular computer, composed of individual panels to perform different functions. Twenty of these modules were accumulators that could not only add and subtract, but hold a ten digit decimal number in memory. Numbers were passed between these units across several 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, depending on the sign of a computed result.

By the end of its operation in 1956, ENIAC contained 18,000 vacuum tubes, 7,200 crystal diodes, 1,500 relays, 70,000 resistors, 10,000 capacitors, and approximately 5,000,000 hand soldered joints. It weighed more than , was roughly tall, deep, and long, occupied and consumed 150 kW of electricity. 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, such as the IBM 405. While ENIAC had no system to store memory in its inception, these punch cards could be used for external memory storage. In 1953, a 100 word magnetic core memory built by the Burroughs Corporation was added to ENIAC. ENIAC used ten position ring counters to store digits; each digit required 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 electronically emulate the operation of the digit wheels of a mechanical adding machine. ENIAC had 20 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) per 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 arithmetic with double the precision, but the accumulator carry circuit timing prevented the wiring of three or more for even higher precision. ENIAC used four of the accumulators (controlled by a special multiplier unit) to perform up to 385 multiplication operations per second; five of the accumulators were controlled by a special divider/square rooter unit to perform up to 40 division operations per second or three square root operations per second. The other nine units in ENIAC were the initiating unit (started and stopped the machine), the cycling unit (used for synchronizing the other units), the master programmer (controlled loop sequencing), the reader (controlled an IBM punch card reader), the printer (controlled an IBM card punch), the constant transmitter, and three function tables.

The references by Rojas and Hashagen (or Wilkes) compared to modern supercomputers' petascale and exascale computing power.

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. Several tubes burned out almost every day, leaving ENIAC 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. Engineers reduced ENIAC's tube failures to the more acceptable rate of one tube every two days. According to an interview in 1989 with Eckert, "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.

ENIAC could be programmed to perform complex sequences of operations, including loops, branches, and subroutines. However, instead of the stored program computers that exist today, ENIAC was just a large collection of arithmetic machines, which originally had programs set up into the machine by a combination of plugboard wiring and three portable function tables (containing 1,200 ten way switches each). The task of taking a problem and mapping it onto the machine was complex, and usually took weeks. Due to the complexity of mapping programs onto the machine, programs were only changed after huge numbers of tests of the current program. After the program was figured out on paper, the process of getting the program into ENIAC by manipulating its switches and cables could take days. This was followed by a period of verification and debugging, aided by the ability to execute the program step by step. A programming tutorial for the modulo function using an ENIAC simulator gives an impression of what a program on the ENIAC looked like. ENIAC's six primary programmers, Kay McNulty, Betty Jennings, Betty Snyder, Marlyn Wescoff, Fran Bilas and Ruth Lichterman, not only determined how to input ENIAC programs, but also developed an understanding of ENIAC's inner workings. The programmers were often able to narrow bugs down to an individual failed tube which could be pointed to for replacement by a technician.

During World War II, while the U. S. Army needed to compute ballistics trajectories, many women were interviewed for this task. At least 200 women were hired by the Moore School of Engineering to work as "computers" and six of them were chosen to be the programmers of ENIAC. Betty Holberton, Kay McNulty, Marlyn Wescoff, Ruth Lichterman, Betty Jean Jennings, and Fran Bilas, programmed the ENIAC to perform calculations for ballistics trajectories electronically for the Army's Ballistic Research Laboratory. While men having the same education and experience were designated as "professionals", these women were unreasonably designated as "subprofessionals", though they had professional degrees in mathematics, and were highly trained mathematicians. However, some of the women did not receive recognition for their work on the ENIAC in their entire lifetimes. After the war ended, the women continued to work on the ENIAC. Their expertise made their positions difficult to replace with returning soldiers. These early programmers were drawn from a group of about two hundred women employed as computers at the Moore School of Electrical Engineering at the University of Pennsylvania. The job of computers was to produce the numeric result of mathematical formulas needed for a scientific study, or an engineering project. They usually did so with a mechanical calculator. The women studied the machine's logic, physical structure, operation, and circuitry in order to not only understand the mathematics of computing, but also the machine itself. This was one of the few technical job categories available to women at that time. Betty Holberton (née Snyder) continued on to help write the first generative programming system (SORT/MERGE) and help design the first commercial electronic computers, the UNIVAC and the BINAC, alongside Jean Jennings. McNulty developed the use of subroutines in order to help increase ENIAC's computational capability. Herman Goldstine selected the programmers, whom he called operators, from the computers who had been calculating ballistics tables with mechanical desk calculators, and a differential analyzer prior to and during the development of ENIAC. Under Herman and Adele Goldstine's direction, the computers studied ENIAC's blueprints and physical structure to determine how to manipulate its switches and cables, as programming languages did not yet exist. Though contemporaries considered programming a clerical task and did not publicly recognize the programmers' effect on the successful operation and announcement of ENIAC, McNulty, Jennings, Snyder, Wescoff, Bilas, and Lichterman have since been recognized for their contributions to computing. The "programmer" and "operator" job titles were not originally considered professions suitable for women. The labor shortage created by World War II helped enable the entry of women into the field. However, the field was not viewed as prestigious, and bringing in women was viewed as a way to free men up for more skilled labor. Essentially, women were seen as meeting a need in a temporary crisis. For example, the National Advisory Committee for Aeronautics said in 1942, "It is felt that enough greater return is obtained by freeing the engineers from calculating detail to overcome any increased expenses in the computers' salaries. The engineers admit themselves that the girl computers do the work more rapidly and accurately than they would. This is due in large measure to the feeling among the engineers that their college and industrial experience is being wasted and thwarted by mere repetitive calculation". Following the initial six programmers, an expanded team of a hundred scientists was recruited to continue work on the ENIAC. Among these were several women, including Gloria Ruth Gordon. Adele Goldstine wrote the original technical description of the ENIAC.

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 National Laboratory, became aware of the ENIAC. In December 1945, the ENIAC was used to calculate thermonuclear reactions using equations. The data was used to support research on building a hydrogen bomb.

Related to ENIAC's role in the hydrogen bomb was its role in the Monte Carlo method becoming popular. Scientists involved in the original nuclear bomb development used massive groups of people doing huge numbers of calculations ("computers" in the terminology of the time) to investigate the distance that neutrons would likely travel through various materials. John von Neumann and Stanislaw Ulam realized the speed of ENIAC would allow these calculations to be done much more quickly. The success of this project showed the value of Monte Carlo methods in science.

A press conference was held on February 1, 1946, and the completed machine was announced to the public the evening of February 14, 1946, featuring demonstrations of its capabilities. Elizabeth Snyder and Betty Jean Jennings were responsible for developing the demonstration trajectory program, although Herman and Adele Goldstine took credit for it. The machine was formally dedicated the next day at the University of Pennsylvania. None of the women involved in programming the machine or creating the demonstration were invited to the formal dedication nor to the celebratory dinner held afterwards. The original contract amount was $61,700; the final cost was almost $500,000 (approximately 487000.0 in 1943 is equivalent to about <calculated amount> in recent years). 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, when it was retired in favor of the more efficient EDVAC and ORDVAC computers. the Pentagon invited "the top people in electronics and mathematics from the United States and Great Britain"

ENIAC was a one of a kind design and was never repeated. The freeze on design in 1943 meant that it lacked some innovations that soon became well developed, notably the ability to store a program. Eckert and Mauchly started work on a new design, to be later called the EDVAC, which would be both simpler and more powerful. In particular, in 1944 Eckert wrote his description of a memory unit (the mercury delay line) which would hold both the data and the program. John von Neumann, who was consulting for the Moore School on the EDVAC, sat in on the Moore School meetings at which the stored program concept was elaborated. Von Neumann wrote up an incomplete set of notes (First Draft of a Report on the EDVAC) which were intended to be used as an internal memorandum—describing, elaborating, and couching in formal logical language the ideas developed in the meetings. ENIAC administrator and security officer Herman Goldstine distributed copies of this First Draft to a number of government and educational institutions, spurring widespread interest in the construction of a new generation of electronic computing machines, including Electronic Delay Storage Automatic Calculator (EDSAC) at Cambridge University, England and SEAC at the U. S. Bureau of Standards. after which programming was done by setting the switches. The idea has been worked out in several variants by Richard Clippinger and his group, on the one hand, and the Goldstines, on the other, and it was included in the ENIAC patent. Clippinger consulted with von Neumann on what instruction set to implement. The "first production run" of the new coding techniques on the Monte Carlo problem followed in April. After ENIAC's move to Aberdeen, a register panel for memory was also constructed, but it did not work. A small master control unit to turn the machine on and off was also added. The programming of the stored program for ENIAC was done by Betty Jennings, Clippinger, Adele Goldstine and others.

Mechanical computing machines have been around since Archimedes' time (see: Antikythera mechanism), but the 1930s and 1940s are considered the beginning of the modern computer era. ENIAC was, like the IBM Harvard Mark I and the German Z3, able to run an arbitrary sequence of mathematical operations, but did not read them from a tape. Like the British Colossus, it was programmed by plugboard and switches. ENIAC combined full, Turing complete programmability with electronic speed. The Atanasoff–Berry Computer (ABC), ENIAC, and Colossus all used thermionic valves (vacuum tubes). ENIAC's registers performed decimal arithmetic, rather than binary arithmetic like the Z3, the ABC and Colossus. Like the Colossus, ENIAC required rewiring to reprogram until April 1948. In June 1948, the Manchester Baby ran its first program and earned the distinction of first electronic stored program computer. Though the idea of a stored program computer with combined memory for program and data was conceived during the development of ENIAC, it was not initially implemented in ENIAC because World War II priorities required the machine to be completed quickly, and ENIAC's 20 storage locations would be too small to hold data and programs.

The Z3 and Colossus were developed independently of each other, and of the ABC and ENIAC during World War II. Work on the ABC at Iowa State University was stopped in 1942 after John Atanasoff was called to Washington, D. C., to do physics research for the U. S. Navy, and it was subsequently dismantled. The Z3 was destroyed by the Allied bombing raids of Berlin in 1943. As the ten Colossus machines were part of the UK's war effort their existence remained secret until the late 1970s, although knowledge of their capabilities remained among their UK staff and invited Americans. ENIAC, by contrast, was put through its paces for the press in 1946, "and captured the world's imagination". Older histories of computing may therefore not be comprehensive in their coverage and analysis of this period. All but two of the Colossus machines were dismantled in 1945; the remaining two were used to decrypt Soviet messages by GCHQ until the 1960s. The public demonstration for ENIAC was developed by Snyder and Jennings who created a demo that would calculate the trajectory of a missile in 15 seconds, a task that would have taken several weeks for a human computer. decision of the landmark federal court case Honeywell, Inc. v. Sperry Rand Corp The decision included: that the ENIAC inventors had derived the subject matter of the electronic digital computer from Atanasoff; gave legal recognition to Atanasoff as the inventor of the first electronic digital computer; and put the invention of the electronic digital computer in the public domain.

ENIAC was named an IEEE Milestone in 1987. In 1996, in honor of the ENIAC's 50th anniversary, The University of Pennsylvania sponsored a project named "ENIAC on a Chip", where a very small silicon computer chip measuring 7.44 mm by 5.29 mm was built with the same functionality as ENIAC. Although this 20 MHz chip was many times faster than ENIAC, it had but a fraction of the speed of its contemporary microprocessors in the late 1990s. In 1997, the six women who did most of the programming of ENIAC were inducted into the Technology International Hall of Fame. The role of the ENIAC programmers is treated in a 2010 documentary film titled Top Secret Rosies: The Female "Computers" of WWII by LeAnn Erickson. A 2014 documentary short, The Computers by Kate McMahon, tells of the story of the six programmers; this was the result of 20 years' research by Kathryn Kleiman and her team as part of the ENIAC Programmers Project. In 2022 Grand Central Publishing released Proving Ground by Kathy Kleiman, a hardcover biography about the six ENIAC programmers and their efforts to translate block diagrams and electronic schematics of the ENIAC, then under construction, into programs that would be loaded into and run on ENIAC once it was available for use. In 2011, in honor of the 65th anniversary of the ENIAC's unveiling, the city of Philadelphia declared February 15 as ENIAC Day. The ENIAC celebrated its 70th anniversary on February 15, 2016.