D825-a multiple-computer system for command and control1
James P. Anderson / Samuel A. Hoffman / Joseph Shifman / Robert I. Williams
The D825 Modular Data Processing System is the result of a Burroughs study, initiated several years ago, of the data processing requirements for command and control systems. The D825 has been developed for operation in the military environment. The initial system, constructed for the Naval Research Laboratory with the designation AN/GYK-3(V), has been completed and tested. This paper reviews the design criteria analysis and design rationale that led to the system structure of the D825. The implementation and operation of the system are also described. Of particular interest is the role that developed for an operating system program in coordinating the system components.
Functional requirements of command and control data processing
By "command and control system" is meant a system having the capacity to monitor and direct all aspects of the operation of a large man and machine complex. Until now, the term has been applied exclusively to certain military complexes, but could as well be applied to a fully integrated air traffic control system or even to the operation of a large industrial complex. Operation of command and control systems is characterized by an enormous quantity of diverse but interrelated tasks-generally arising in real time-which are best performed by automatic data-processing equipment, and are most effectively controlled in a fully integrated central data processing facility. The data processing functions alluded to are those typical of data processing, plus special functions associated with servicing displays, responding to manual insertion (through consoles) of data, and dealing with communications facilities. The design implications of these functions will be considered here.
Availability criteria. The primary requirement of the data-processing facility, above all else, is availability. This requirement, essentially a function of hardware reliability and maintainability, is, to the user, simply the percentage of available, on-line, operation time during a given time period. Every system designer must trade off the costs of designing for reliability against those incurred by unavailability, but in no other application are the costs of unavailability so high as those presented in command and control. Not only is the requirement for hardware reliability greater than that of commercial systems, but downtime for the complete system for preventive maintenance cannot be permitted. Depending upon the application, some greater or lesser portion of the complete system must always be available for primary system functions, and all of the system must be available most of the time.
The data processing facility may also be called upon, except at the most critical times, to take part in exercising and evaluating the operation of some parts of the system, or, in fact, in actual simulation of system functions. During such exercises and simulations, the system must maintain some (although perhaps partially and temporarily degraded) real-life and real-time capability, and must be able to return quickly to full operation. An implication here, of profound significance in system design, is, again, the requirement that most of the system be always available; there must be no system elements (unsupported by alternates) performing functions so critical that failure at these points could compromise the primary system functions.
Adaptability criteria. Another requirement, equally difficult to achieve, is that the computer system must be able to analyze the demands being made upon it at any given time, and determine from this analysis the attention and emphasis that should be given to the individual tasks of the problem mix presented. The working configuration of the system must be completely adaptable so as to accommodate the diverse problem mixes, and, moreover, must respond quickly to important changes, such as might be indicated by external alarms or the results of internal computations (exceeding of certain thresholds, for example), or to changes in the hardware configuration resulting from the failure of a system component or from its intentional removal from the system. The system
1AFIPS Proc. FJCC, vol. 22, pp. 86-96, 1962.