Fig. EPUT-2. An RTM system diagram of an Events Per Unit Time\EPUT meter.
KEYWORDS: Parallelism, time-sharing, polling
This design problem illustrates how the EPUT meter design of the previous problem might be modified such that a single system would give the appearance of being many independent EPUT meters. Such a system falls into the space of time-shared systems design, the main objective being the design of a single system which behaves as n independent systems. The gain from this design approach is that it is usually more economical to have a single system handle n inputs than to have n independent systems handle one input each. A drawback to the centralized, time-shared approach is that unless such systems are handling a close-to-capacity number of inputs, they are unnecessarily complex and expensive.
The technique of time-sharing usually focuses upon a resource which must be shared among all processes in the system. The trade-off between n independent systems and a single time-shared system is that each process in the time-shared system can use only 1/n of the shared resource; expense has been traded for performance. Of course time-shared systems are not constrained to have a single instance of a shared resource; the n processes may share several instances of the same resource (approaching n independent systems in the limit), or the processes could share the services of many resources combined to form a single system.
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