Stored Program Digital Computers

With the advent of the stored-program digital computer a minor revolution occurred in quantum chemistry. The integrals appearing in the models being used for small molecules were actually evaluated and it became clear that molecules were enormously more complicated than had been anticipated. The oversimplified valence bond and molecular orbital methods often gave qualitatively ridiculous results when taken literally (11). 

By way of analogy, the ALU may be thought of as a super adding machine with its keys commanded automatically by the control signals developed in the instruction decoder and the control circuitry. This is essentially how the first stored-program digital computer was conceived. The ALU naturally bears little resemblance to a desktop adder. The major difference is that the ALU calculates by creating... 

In 1946, Max Newman (who had woiked with Flowers on Colossus) went on to estabhsh the Royal Society Computing Machine Laboratory at Manchester University, where with colleagues he built the world s first electronic stored-program digital computer, called the Manchester Baby, which was first operational in June 1948. Their development led to the world s first commercially available general-purpose electronic computer, called the Ferranti Mark 1. The first was delivered in February 1951. 

The first US-produced commercially available electronic stored-program digital computer was UNI VAC 1, which was developed by Eckert and Mauchly and was delivered to the US Census Bureau in March 1951. 

The output of the NMR spectrometer must be transformed from an analog electrical signal into digital information that can be stored in the computer s dedicated computer. The minicomputers used in NMR spectroscopy have memory used for data accumulation, programs for manipulating the data, and storage devices to store large collections of data for future or additional manipulation into useful spectral results. 

In a digital computer-control system, the feedback controller has a pulse transfer function. What we need is an equation or algorithm that can be programmed into the digital computer. At the sampling time for a given loop, the computer looks at the current process output x, compares it to a setpoint, and calculates a current value of the error. This error, plus some old values of the error and old values of the controller output or manipulated variable that have been stored in computer memory, are then used to calculate a new value of the controller output m,. 

The Monte Carlo method is especially suited for use on a digital computer, particularly one of the stored-program type. The mathematical model and the distribution function, even if quite complicated, can be expressed on the computer and the necessary calculations are highly repetitive. Also, random numbers (or rather pseudorandom numbers) can be synthesized so that the computer procedure becomes fully automatic and self-contained (M9, S5). 

This problem can be partially resolved by using a digital computer in which integration is performed after the spectrum is stored in the memory. Some careful base-line correction can be made before trial integration. The Fabri-tek 1070 instrument computers are hard-wired programmed for such operation, and a thorough examination performed in our laboratory indicated that a normal integration uncertainty of less than 1% can be obtained with this computer. 

The next two sections of this chapter treat the technical history of computational chemistry, namely the development of the hardware, concepts, and methods used in the field. We discuss first the chemists earliest uses of the computer as a research tool in the 1950s. The first stored program electronic digital computers became available in the early 1950s in chemistry, as in other branches of science, these devices were initially deployed as calculating engines. Next we deal with the expansion of the field of computational chemistry during... 

Sequential programming (e.g. stored-program on digital computer)... 

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