Chapter 1

THE TASKS AND THE COMPUTERS

A. INTRODUCTION

On-line data-acquisition computer systems are made in a wide range of types and sizes. In all cases at least one electronic computer is involved--a stored-program machine--because wired-program devices such as pulse-height analyzers are not considered to be computers. The rest of the system typically consists of input/output (I/O) devices such as analog-to-digital converters (ADC's), printers, cathode-ray oscilloscopes, plotters, and control devices, which may include, in addition to the console typewriter, switch boxes to simplify the control of special types of operations and perhaps a set of logic circuits associated with the input system, used to provide preliminary selection of incoming data. In a small but increasing number of cases a computer is seen dedicated entirely to a "process-control" application such as the automatic adjustment of the shim coils of a variable-energy cyclotron or the control of data acquisition in a nuclear-scattering experiment, adjustments such as changing the angle of observation being made essentially under direct automatic control of the computer. The smallest on-line systems use the smallest commercially available computers; the largest use computers bigger than those which until recently served most computing centers. Large systems sometimes include one or more satellite computers. The cost of individual systems ranges from $25,000 to $1,000,000, approximately. The total cost of computer systems in low-energy nuclear laboratories is estimated by now to have reached about $20,000,000. (There has been a larger expenditure in the high-energy nuclear field, where computer systems have been employed extensively for some years longer and where experiments are so expensive that the economic advantages of computer use were quickly recognized.)

B. THE TASKS

We first list the main uses to which on-line computer systems have been put. We start with the simple operations, which we call Class 1.

_Class 1 operations_:

a. Accepting digital data from external devices and storing it in computer memory.

b. Preliminary processing of incoming data, on-line, before storage. This usually involves only operations of logic and simple arithmetic.