FRANK L. HASSLER Defense Communications Agency
INTRODUCTION
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As technology has provided ever more capable electronic computers, communication methods, and sensing elements, system designers have been working to implement information systems on a scale commensurate with the tools.
The purpose of this paper is to examine in general the experience ob-tained with large systems. In this examination, the word "system" means the composite of sensing elements, communications, and automatic data-processing (ADP) equipment, personnel, and procedures used to ac-complish the broad functional mission of the complex. All the system examples used will contain all of these components, but emphasis will be placed upon the ADP aspects of the system.
In a discussion of experience with large scale systems, a distinction will be made between systems with known, repetitive functions, sensor based systems, and command systems. Each type is characterized by different degrees of complexity, cost, uncertainty, etc., and the differences create marked variations in performance.
SYSTEMS OF KNOWN REPETITIVE FUNCTIONS (CLASS I)
Systems with known repetitive functions are exemplified by library systems, inventory control and accounting systems, or systems performing scientific computation. The ADP support tends toward scheduled run, batch processing complexes.
System costs may range from one to one hundred million dollars and will in most cases represent a saving over costs for a completely manual system to perform the same function. For example: A complex of small computers on a regional basis to handle central accounting for a firm with up to 107 transactions per month might cost more than $50 million.
The startup time for systems in this class may range from one to two years. This is based upon the assumption that the functions are well known, and that programming time and hardware implementation times
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are about equal. Finally, it is assumed that some means of data inputting is already existent in a form that requires little modification.
The degree of automation is usually high for such systems, at least in terms of data organization, computation, and formatting of outputs in useful form. Sophistication of data inputting is also possible but not widely used at present.
The utilization of the ADP support to the system is high in the sense that it is easy to tailor it to the expected loads and it is relatively easy to add new capacity when required. As a result, high design efficiencies are possible.
The performance of a Class I system is good to excellent in the sense that the information processing is precise and rapid. As a result, some applications can be undertaken that are not feasible with manual methods.
When comparing Class I systems as defined here with other types it must be remembered that these systems are the least complex. Function-ally, the logical operations performed usually require one to three men in a manual system. While the system may handle many problems, the problems generally are not interrelated and data correlation is low. Tech-nically, the system complexity depends upon the load and degree of auto-mation of the data-input subsystem.
SENSOR BAS,ED SYSTEMS (CLASS II) The majority of sensor based systems serve military applications. Ex-amples are: BMEWS (Ballistic Missile Early Warning System), the SAGE Air Defense System and NUDETS (Nuclear Detonation Detection Sys-tem). Missile range instrumentation provides a nonmilitary example.
These systems have many highly sophisticated electronic sensing elements, elaborate data communication subsystems and large, rapid computers.
Costs for sensor based systems are very high. BMEWS probably cost about $1.0 billion. SAGE costs are more than twice as great. In com-paring costs with other classes it should be remembered that the quoted costs are total system costs, the bulk of which are for sensors and com-munications.
Startup times are long. BMEWS, begun in the fall of 1957, took more than three years to become fully operational. SAGE required four to five years. For NUDETS, three years was required to implement a proto-type installation.
In sensor based systems the degree of automation is very high. In most instances automation is essential if the system functions are to be per-formed within a meaningful span of time.
LARGE SYSTEMS 131 The utilization of the system is high to perform the function for which it was designed. However, in military applications, the functions of opera-tional importance often change markedly. Modifications of design func-tions or provision of added capacity for sensor based systems are per-formed only with the greatest of difficulty. This is even more pronounced for the ADP aspect of the system.
The performance of the systems is generally good from the point of view of technology. That is, the systems do perform their designed func-tions rapidly and accurately in a real-time mode that would be impossible with manual methods. Performance is generally more questionable from an operational point of view because of the tendency of the systems to become obsolete in a rapidly changing world. For military applications in particular, not only do the operational functions change but also threat changes have had dramatic effect upon the vulnerability of the system, and hence upon its usefulness.
The complexity of sensor based systems is significantly higher than in the case of Class I systems. Functionally the complexity would require the equivalent of ten to twenty people in a manual system [e.g., two radar operators, two communications officers, a track analyst, a weapons spe-cialist, a weather officer, etc.].
The technical complexity is far greater than in the previous case. The data rates are more rapid, the processing timing requirements far more stringent, the logical complexity far greater, etc.
Given the complexity of sensor based systems, cost cannot be viewed as a negative aspect of experience. Complex technical performance is costly.
It is probable that design efficiency or clever use of technology would have only second order effect on cost.
Similarly, within reasonable limits of available technology, startup times are governed by the lead times in equipment design and acquisition.
For example: in BMEWS, communication construction times were gen-erally the pacing items, not radar development.
Given the complexity of sensor based systems, performance, particu-larly for nonmilitary applications, can't accurately be counted as negative.
The cost of obsolescence is the price of progress. In hardware, general-purpose design has long been used to combat change in functional re-quirements. In computer programming, general purpose data handling procedures are somewhat newer and are being used to lengthen the period of useful operation.
The crucial point constantly under debate today between system critics and defenders is "whether or not we must have complex sensor based systems to begin with?" The critics insist that in view of the cost and time taken for what is provided, some theoretically less capable approach
might have provided as much performance with much shorter time delay and for far less cost. It would appear in some cases that the critics are winning the argument, for the automated approach is being augmented with or abandoned in favor of methods employing decentralized, less automated information handling.