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ENIAC, short for '''Electronic Numerical Integrator And Computer''',1 was the first large-scale, electronic, digital computer capable of being reprogrammed to solve a full range of computing problems,Shurkin, Joel, ''Engines of the Mind: The Evolution of the Computer from Mainframes to Microprocessors'', 1996, ISBN 0-393-31471-5 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 contract was signed on , 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 Bob Shaw (function tables), Chuan Chu (divider/square-rooter), Kite Sharpless (master programmer), Arthur Burks (multiplier), Harry Huskey (reader/printer), and Jack Davis (accumulators). . "U.S. Army Photo" from the archives of the ARL Technical Library. Left: .]] DESCRIPTION ENIAC was massive compared to modern PC standards. It contained 17,468 Vacuum Tube s, 7,200 crystal Diode s, 1,500 Relay s, 70,000 Resistor s, 10,000 Capacitor s and around 5 million hand- Solder ed joints. It weighed 30 Short Ton s (27 t), was roughly 8 feet (2.4 m) by 3 feet (0.9 m) by 100 feet (30 m), took up 1800 square feet (167 m&2), 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 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'' (started and stopped the machine), the ''Cycling Unit'' (synchronized the other units), the ''Master Programmer'' (controlled "loop" sequencing), the ''Reader'' (controlled an IBM punch card reader), the ''Printer'' (controlled an IBM punch card punch), the ''Constant Transmitter'', and three ''Function Tables''. The reference by Rojas and Hashagen gives more details about the times for operations, which differ somewhat from those 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. 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 Accumulator s were made of 6SN7 Flip-flops , while 6L7s, 6SJ7s, 6SA7s and 6AC7s were used in logic functions. Numerous 6L6 s and 6V6 s 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). 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 ( {Link without Title} ). 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 , an idea proposed by John Von Neumann . Three digits of one accumulator (6) was used as the program counter, another accumulator (15) was used as the main accumulator, another accumulator (8) was used as the address pointer for reading data from the function tables, and most of the other accumulators (1-5,7,9-14,17-19) 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 and eliminated the ability of parallel computation, but as it also reduced the reprogramming time to hours instead of days, it was considered well worth the loss of performance. Also analysis had shown that due to differences between the electronic speed of computation and the electromechanical speed of input/output, almost any practical real world problem was completely I/O Bound even without making use of the original machine's parallelism and most would still be I/O bound even after the speed reduction from this modification. 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 See Also: History of computing hardware 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 ABC, ENIAC and Colossus all used Thermionic Valves (vacuum Tubes) . ENIAC's registers performed decimal arithmetic, 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 Colossus and ENIAC were developed independently and in secret as part of each country's war effort in World War II . 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 dismantled by Iowa State University , after John Atanasoff was called to Washington, D.C. to do physics research for the U.S. Navy. 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. Patent See Also: Honeywell v. Sperry Rand For a variety of reasons (including Mauchly's June 1941 examination of the Atanasoff–Berry Computer , prototyped in 1939 by John Atanasoff and Clifford Berry ), 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 and providing legal recognition to Atanasoff as the inventor of the electronic digital computer. Controversy still surrounds the meaning of the decision. PARTS ON DISPLAY ]] The School of Engineering and Applied Science at the University Of Pennsylvania has four of the original forty panels and one of the three function tables of the ENIAC. The Smithsonian has five 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 at Aberdeen Proving Ground ( Aberdeen, Maryland ), where ENIAC was used, has one of the function tables. As Of 2004 , a chip of silicon measuring 0.02 inches (0.5 mm) square holds the same capacity as the ENIAC, which occupied a large room. SEE ALSO
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