Electronic numerical integrator and calculator

FIGURE 8.1 The Electronic Numerical Integrator and Calculator (ENIAC) and its inventor, J. Presper Eekert, circa 1946. ENIAC was the world s first electronic computer. Courtesy, UNISYS Corporation. 

Digital computers were first built at Harvard University (Aiken s53 Automatic Sequence Controlled Calculator, Mark I, 1939-1944) and at the University of Pennsylvania by Eckert54 and Mauchly55 (Electronic Numerical Integrator and Calculator, ENIAC, 1946) they used vacuum tubes instead of the cumbersome and slow mechanical switches. ENIAC morphed into an Eckert-Mauchly design of BINAC, which was sold to Remington Rand and became Univac I. 

If and when a Josephson junction computer is built, the junction s size and low power dissipation would allow manufacturers to put more guts and gas into their machines. Their cycle times—the time required for a chip to perform one task—would be substantially shortened. Such a computer might, in fact, fill a cube only 2 inches on a side and operate more than fifty times faster than the best that are available today. No mean feat, considering that the world s first all-electronic computer, ENIAC (for Electronic Numerical Integrator and Calculator), covered some 1,500 square feet of floor space at the University of Pennsylvania, where it had its maiden run in 1946, was jam-packed with some twenty thousand vacuum tubes, and weighed in at more than 30 tons. Moreover, its computations were measured in seconds—not a nanosecond, a picosecond (a trillionth of a second), or a femtosecond (a quadrillionth of a second), the measurements computer designers are accustomed to shooting for today. 

The first electronic computer ENIAC (Electronic Numerical Integrator and Calculator) developed in 1946 at the University of Pennsylvania had about 18,000 thermionic valves and consumed about 150 kW of electrical power. It was a huge machine weighing over 25,000 kg and filled a room. Initially, it was used for calculating artillery firing tables for the US Army s Ballistic Research Laboratory. 

In the 1940 s, British intelligence created the first computer, Colossus. After World War II, the British destroyed Colossus. Two Americans at the University of Pennsylvania are credited with creating the first American computer in 1945. It was named the Electronic Numerical Integrator and Calculator (ENIAC). It was able to easily decrypt manual and Enigma ciphers. 

Atanasoff/Berry Computer built in the early 1940s at Iowa State University, or J. Prosper Eckert and John Mauchly for their ENIAC (Electronic Numerical Integrator and Calculator) built in the mid-1940s at the Moore School of the University of Pennsylvania, because Mauchly had briefly visited Atanasoff before he built the ENIAC. Its basic principles were enunciated in a memorandum written by von Neumann in 1945 and, largely because of this widely circulated report, von Neumann s name alone has come to be associated with concept of the stored-program computer. 

Whereas much of the UK-based wartime work was kept secret, work progressed in the USA in parallel with the UK work, and in a more open fashion. Electronic numerical integrator and calculator (ENIAC) was conceived and designed by John Mauchly (1907-1980) and John Adam Prosper Pres Eckert (1919-1995), following a 1942 memo from Mauchly proposing a general-purpose electronic computer. A contract was received from the US Army in 1943, and the completed machine was announced to the pubhc in Eebruary 1946. It used some 17,000 thermionic valves and weighed about 27 tonnes. Vacuum tube failure rate was such that its availability was only about fifty percent. Input was via an IBM card reader. 

The most widespread manifestation of electronics has been in personal computers and calculators. Although mechanical calculating machines have been available for hundreds of years, and ENIAC (electronic numerical integrator and computer) was built using over 19,000 vacuum tubes, it was not until the advent of low-cost electronics that computers became feasible for widespread use. Since that time, they have become ubiquitous, not only as stand-alone products, but also incorporated into products ranging from automobiles to military weapons. 

The universal function x(x) obtained by numerical integration and valid for all neutral atoms decreases monotonically. The electron density is similar for all atoms, except for a different length scale, which is determined by the quantity b and proportional to Z. The density is poorly determined at both small and large values of r. However, since most electrons in complex atoms are at intermediate distances from the nucleus the Thomas-Fermi model is useful for calculating quantities that depend on the average electron density, such as the total energy. The Thomas-Fermi model therefore cannot account for the periodic properties of atoms, but provides a good estimate of initial fields used in more elaborate calculations like those to be discussed in the next section. 

The trick is that the derivative of the difference between the nonrelativistic one-electron integrals and the one-electron DKH integrals is calculated numerically. Since one-electron integrals are easy to calculate and require negligible computing time, they can easily be calculated for distorted structures, so that the derivative can be evaluated using finite-difference techniques. An... 

For calculational purposes, the basic quantities rM, Q and Oe(rJ ) are obtained as follows a) From accurate atomic wavefunctions, the electron density is obtained by numerical integration (b) with the electron density at any point at hand, the values are obtained by the simple reading of the distance at which p r) attains the critical value of 0.00872 electron units and (c) the central charge and the RF potential are readily obtained in terms of ty and Og(/>) via Eqs (11) and (15), respectively. 

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