ENIAC
ENIAC 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. 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, 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.
Development and design
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,. The conception of ENIAC began in June 1941, when Friden calculators and differential analyzers were used by the United States Army Ordnance Department to compute firing tables for artillery, which was done by graduate students under John Mauchly's supervision. Mauchly began to wonder if electronics could be applied to mathematics for faster calculations. He partnered with research associate J. Presper Eckert, as Mauchly wasn't an electronics expert, to draft an electronic computer that could work at an excellent pace. Later, in August 1942, Mauchly proposed an all-electronic calculating machine that could help the U.S. Army calculate complex ballistics tables. The U.S. Army Ordnance accepted their plan, giving the University of Pennsylvania a six-months research contract for $61,700. 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 Goldstine persuaded the Army to fund the project, which put him in charge to oversee it for them. Assembly of the computer began in June 1944. Later, in September of that year, Eckert and Mauchly completed their conception of the computer. Construction was complete in May 1945, and testing began at the Moore School. Later, in November of that year, the duo, along with John Brainerd and Herman Goldstine, issued the first confidentially published report on the computer, which describes how it functioned and the methods by which it was programmed.ENIAC was designed by Ursinus College physics professor John Mauchly and J. Presper Eckert of the University of Pennsylvania. The team of design engineers assisting the development included Robert F. Shaw, Jeffrey Chuan Chu, Thomas Kite Sharpless, Frank Mural, Arthur Burks, Harry Huskey and Jack Davis. Significant development 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. 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.
Components
By the end of its operation in 1956, ENIAC contained 18,000 vacuum tubes, 7,200 crystal diodes, 6,000 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 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 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, the cycling unit, the master programmer, the reader, the printer, the constant transmitter, and three function tables.
Operation times
The references by Rojas and Hashagen give more details about the times for operations, which differ somewhat from those stated above.The basic machine cycle was 200 microseconds, 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 took d+4 cycles, so the multiplication of a 10-digit number by 10-digit number took 14 cycles, or 2,800 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 cycles, where d is the number of digits in the result. So a division or square root took up to 143 cycles, or 28,600 microseconds—a rate of 35 per second. If the result had fewer than ten digits, it was obtained faster.
ENIAC was able to process about 500 FLOPS, compared to modern supercomputers' petascale and exascale computing power.
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.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.
Programming
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. 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.
Programmers
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 "professionals", these women were designated "subprofessionals", though they had professional degrees in mathematics and were highly trained mathematicians.These women were not "refrigerator ladies", i.e., models posing in front of the machine for press photography, as then computer scientist undergrad Kathryn Kleiman discovered in her own research as opposed to what she was told by a historian in computing. 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. Later in the 1990s, Kleiman learned that most of the ENIAC programmers were not invited to the ENIAC's 50th anniversary event. So she made it her mission to track them down and record their oral histories. "They were shocked to be discovered," Kleiman says. "They were thrilled to be recognized, but had mixed impressions about how they felt about being ignored for so long." Kleiman released a book on the six female ENIAC programmers in 2022.
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 continued on to help write the first generative programming system 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. Three of the current Army supercomputers, Jean, Kay, and Betty, are named after Jean Bartik, Kay McNulty, and Betty Snyder respectively.
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.