Encyclopedia
ENIAC, short for
Electronic Numerical Integrator and Computer, was the first large-scale, electronic, digital computer capable of being reprogrammed to solve a full range of computing problems, although earlier computers had been built with some of these properties. ENIAC was designed and built to calculate
artillery firing tables for the
U.S. Army's Ballistics Research Laboratory. The first problems run on the ENIAC however, were related to the design of the
hydrogen bomb.
The contract was signed on June 5, 1943 and
Project PX was constructed by
Penn's Moore School of Electrical Engineering from July, 1943. It was unveiled on February 15, 1946 at the University of Pennsylvania, having cost almost $500,000. ENIAC was shut down on November 9, 1946 for a refurbishment and a memory upgrade, and was transferred to the Aberdeen Proving Ground,
Maryland in 1947. There, on July 29 of that year, it was turned on and would be in continuous operation until 11:45 p.m. on October 2, 1955.
ENIAC was conceived and designed by John William Mauchly and J. Presper Eckert of the
University of Pennsylvania. The patent for the ENIAC, granted in 1964, was voided by the 1973 decision of the landmark federal court case
Honeywell v. Sperry Rand, putting the invention of the electronic digital computer in the
public domain.
Description
Physically, ENIAC was massive. It 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 , was roughly 8 feet by 3 feet by 100 feet , took up 1800 square feet , and consumed 150 kW of power. Input was possible from an IBM card reader, while an IBM card punch was used for output. These cards could be used to produce printed output offline using an
IBM accounting machine, probably the
IBM 405.
ENIAC used ten-position ring counters to store digits; each digit used 36 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 and could perform 5,000 simple addition or subtraction operations between any selected pair of them every second . It was possible to wire the carry of one accumulator into another 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 and could perform 385 multiplication operations per second. The ENIAC used five of the accumulators controlled by a special
Divider/Square-Rooter unit and could perform forty 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. Design engineers included Bob Shaw , Chuan Chu , Kite Sharpless , Arthur Burks , Harry Huskey , and Jack Davis .
The reference by Rojas and Hashagen gives more details about the times for operations, which differ somewhat from those above. The basic clock 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 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 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.
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 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 . This failure rate was remarkably low, and stands as a tribute to the precise engineering of ENIAC.
Programmability
The six women who did most of the programming of ENIAC by manipulating its switches and cables 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.
Eckert and Mauchly took the experience they gained and founded the Eckert-Mauchly Computer Corporation, producing their first computer, BINAC, in 1949 before being acquired by
Remington Rand in 1950 and renamed as their
UNIVAC division.
ENIAC was a one-of-a-kind design and was never repeated. The freeze on design in 1943 meant that the computer had a number of shortcomings which were not solved, notably the inability to store a program. But the ideas generated from the work and the impact it had on people such as
John von Neumann were profoundly influential in the development of later computers, initially
EDVAC,
EDSAC and SEAC.
A number of improvements were also made to ENIAC from 1948, including a primitive read-only stored programming mechanism using the Function Tables as program
ROM, an idea proposed by
John von Neumann. Three digits of one accumulator was used as the program counter, another accumulator was used as the main accumulator, and most of the other accumulators were just used for data memory. It was first demonstrated as a stored-program computer on September 16 1948, running a program by Adele Goldstine for John von Neumann. This modification reduced the speed of ENIAC by a factor of six, but as it also reduced the reprogramming time to hours instead of days, it was considered well worth the loss of performance. Early in 1952, a high speed shifter was added, which improved the speed for shifting by a factor of five. In July 1953, a 100-word expansion
core memory was added to the system, using binary coded decimal, excess-3 number representation. To support this expansion memory, the ENIAC was equipped with a new Function Table selector, a memory address selector, pulse-shaping circuits, and three new orders were added to the programming mechanism.
Comparison with other early computers
Mechanical and electrical computing machines have been around since the 19th century, but the 1930s and 40s are considered the beginning of the modern computer era.
- The American Atanasoff-Berry Computer was thought by some to be the first electronic digital computer. It implemented binary computation with vacuum tubes but was not general purpose, being limited to solving systems of linear equations. It also did not exploit electronic computing speeds, being limited by an electromechanical memory and an input-output system that was intended to write intermediate results to paper cards.
- The German Z3 was designed in 1941 by Konrad Zuse. It was the first general purpose, electromechanical computer. It was a digital computer using binary math, was Turing-complete and fully programmable by punched tape. Since the computer used relays for all functions it was not electronic.
- The British Colossus computer was designed by Tommy Flowers. Colossus was digital, all-electronic, and could be reprogrammed by rewiring, but was not fully general purpose as it was not Turing-complete.
- Howard Aiken's 1944 Harvard Mark I was programmed by punched tape and used relays.
The ABC, ENIAC and Colossus all used thermionic valves . ENIAC's registers performed decimal, rather than binary, arithmetic like the Z3 or the Atanasoff-Berry Computer.
Until 1948, ENIAC required rewiring to reprogram, like the Colossus. The idea of the
stored-program computer with combined memory for program and data was conceived during the development of the ENIAC, but it was not implemented at that time because World War II priorities required the machine to be completed quickly, and it was realized that 20 storage locations for memory and programs would be much too small.
Priority
The Z3, Colossus and ENIAC were developed independently and in secret as part of each country's war effort in
WWII. The Z3 was destroyed by Allied bombing of Berlin in 1944. The Colossus machines were destroyed in 1945 on
Winston Churchill's orders and their existence remained classified until the 1970s, though knowledge of their capabilities remained among the UK staff and invited Americans. The ABC was abandoned at
Iowa State University, when
John Atanasoff was called to
Washington, DC to do war research. ENIAC, by contrast, was put through its paces for the press in 1946, "and captured the world's imagination". For these reasons, histories of computing formerly mentioned only ENIAC and the Harvard Mark I from this period.
Trivia
The School of Engineering and Applied Science at the
University of Pennsylvania has four of the original 40 panels of the ENIAC. The artifacts on display represent approximately 1/10th of its original size. The
Smithsonian has 5 panels in the
National Museum of American History in Washington D.C. The
Computer History Museum in Mountain View, California has a single panel on display. The
University of Michigan in Ann Arbor has four panels, salvaged by Arthur Burks. The U.S. Army Ordnance Museum also holds some of the ENIAC.
As of 2004, a chip of silicon measuring 0.02 inches square holds the same capacity as the ENIAC, which occupied a large room.
See also
- History of computing
- Other early computers:
References
- H. H. Goldstine, A. Goldstine, The Electronic Numerical Integrator and Computer , 1946
- J. Presper Eckert, The ENIAC
- John W. Mauchly, The ENIAC
- Arthur W. Burks, Alice R. Burks, The ENIAC: The First General-Purpose Electronic Computer
- W. Barkley Fritz, The Women of ENIAC
- J. Presper Eckert, John Mauchly, Outline of plans for development of electronic computers
- Raúl Rojas and Ulf Hashagen, editors, The First Computers: History and Architectures, 2000, MIT Press, ISBN 0-262-18197-5.
Further reading
- Mike Hally, Electronic Brains: Stories from the Dawn of the Computer Age, Joseph Henry Press, 2005. ISBN 0-309-09630-8
- Scott McCartney, ENIAC: The Triumphs and Tragedies of the World's First Computer. Walker & Co, 1999. ISBN 0-8027-1348-3.
- Edmund C. Berkeley, GIANT BRAINS or machines that think. John Wiley & sons, inc., 1949. Chapter 7 Speed—5000 Additions a Second: Moore School's ENIAC
- C.B. Tompkins and J.H Wakelin, High-Speed Computing Devices, McGraw-Hill, 1950.*
External links
- chapter in Karl Kempf, Electronic Computers Within The Ordnance Corps, November 1961
- , Martin H. Weik, Ordnance Ballistic Research Laboratories, 1961
- at the University of Pennsylvania
- Modern photographs of parts of the ENIAC
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- 60th anniversary news story
- Transcript of a video interview with Eckert by David Allison for the National Museum of American History, Smithsonian Institution on February 2, 1988. An in-depth, technical discussion on the ENIAC, including the thought process behind the design.
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- from Ballistic Research Laboratories Report No. 971 December 1955,
- issued in 1964 for ENIAC , also
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