·23-3. Problems in Assigning. Clock.Phases 769 23-4. Minimum-wiring Theory 773
23-5. Wiring Table for the Pedagac 782 23-6. Additional Topics 786
Appendix . 787
Name Index. 807
Subject Index 815
PART 1
INTRODUCTION TO DIGITAL PROGRAMMED SYSTEMS
CHAPTER 1
APPLICATIONS OF DIGITAL COMPUTERS AND CONTROL
1-1. Introduction
The purpose of this chapter is to stimulate the reader to want to know what is in the rest of the book. By illustrating how computers can be applied, we hope to interest the reader in how he might help design and use these remarkable machines. The wide range of potential applica-tions of digital computers and control in all phases of science, industry, and government is truly amazing. In the sciences applications range from mathematics and physics to biology and medicine. The early applications were in engineering and physics, but perhaps the greatest scientific use of computers yet to come is in the biological, medical, and social sciences. In business and industry applications range from auto-matic banking, inventory control, and process control to the precise control of milling machines to produce parts requiring complicated high-tolerance machining and to missile-testing processes. In government applications range from automatic patent searching and post-office sort-ing to large-scale control of defense weapon systems. Present applications are already too numerous to list in a single volume, but they are infini-tesimal compared with the potential future applications. We hope, however, that by presenting brief descriptions of just a few applications we may impart to the reader a better insight into how digital computers and controls are used.
In general a computer can be conceived as a numerical-transformation machine. N umbers are the inputs to it, and the computer transforms these numbers into new numbers, which appear as the outputs:
Input numbers
-> I
computer1->
output numbersFor instance, the input numbers may be the initial conditions of a differential equation; the output numbers will be a table of the functional solutions. Or the input numbers may be readings from an engineering drawing, and the output numbers will be coded instructions to direct a special milling machine. Or the input numbers may be codes that
1
2
represent a patient's symptoms; the output numbers may be codes that represent possible alternative disease diagnoses.
There are two main kinds of electronic computers: digital and analog.
In digital computers the numbers (digits) themselves are handled explic-itly by the computer; an analog computer instead deals with a representa-tion of the numbers, for instance, by voltages, lengths, etc. In this book we are concerned with digital computers only. These can be classified as general-purpose or special-purpose computers. In the first part of this book we shall describe the general-purpose computer; in Part 2 we shall consider some of the special-purpose computers. Special-purpose digital computers are sometimes referred to as digital controls.
The same engineering principles are involved in the design of either general-purpose computers or special-purpose digital-control computers.
Therefore we have used the two terms in the title of the book.
For the purposes of this chapter we have arbitrarily classified computer applications into four categories; many applications can fall into more than one of our categories. First we shall consider numerical solutions to equations. This represents an important class of applications, and undoubtedly it is these applications which makers of the first computers had in mind. The first of these applications described is based on prin-ciples familiar to every electrical engineer, the motion of charged particles in a vacuum. However, the context of the application discussed here has far greater significance. Problems involving the solution to equations are not limited to the physical sciences; equations can be written to describe many biological phenomena as well. The second category is process control: Here the need for digital computers with specialized capabilities becomes apparent. It is probably not an exaggeration to say that the third category came into being because of the great capabili-ties of the computers: this is simulation. Before the advent of computers, simulations (except perhaps laboriously calculated military war games) were rarely even discussed because they were clearly not feasible to perform. However, with the advent of high-speed computers simula-tions have become practical, and great new fields of scientific research have been opened. Most of the present-day computer applications can probably be classed in the fourth category, data processing: Business accounting, statistical reductions, information retrieval, and many other important but routine procedures can be handled by computers.
1-2. Numerical Solution to Equations
Motion of Charged Particles in the Earth's Magnetic Field. Project Argus was a major scientific and military experiment conducted by the United States (Fig. 1-1). Rockets carried a small atomic bomb more than 300 miles above the earth, at this altitude the bomb was exploded, and a resulting thin layer of radiation spread quickly round the globe.
Nuclear and atomic particles were propelled by the exploding bomb and streaked through the vacuum of the universe under forces almost entirely due to the earth's magnetic. field. Some particles moved. toward. t4e
SEC. 1-2] APPLICATIONS OF DIGITAL COMPUTERS AND CONTROL 3.
earth's poles and caused artificial auroras (northern and southern lights).
In order to measure the characteristics of this radiation layer, an earth satellite and other rockets were launched with paths passing through the layer (see Fig. 1-2). Instruments in the satellite and rockets transmitted measurements back to earth. Scientifically the shots rank among man-kind's foremost experiments. They showed that radiation introduced
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