TABLE OF CONTENTS Computer systems architects and designers look for configurations of computer systems elements so that system performance meets desired measures. What this means is that the computer system delivers a quality of service that meets the demands of the user applications. But the measure of this quality of service and the expectation of performance vary depending on who you are. In the broadest context we may mean user response time, ease of use, reliability, fault tolerance, and other such performance quantities. The problem with some of these is that they are qualitative versus quantitative measures. To be scientific and precise in our computer systems performance studies, we must focus on measurable quantitative qualities of a system under study.
There are many possible choices for measuring performance, but most fall into one of two categories: system-oriented or user-oriented measures. The system-oriented measures typically revolve around the concepts of throughput and utilization. Throughput is defined as the average number of items (e.g., transactions, processes, customers, jobs, etc.) processed per unit of measured time. Throughput is meaningful when we also know information about the capacity of the measured entity and the presented workload of items at the entity over the measured time period. We can use throughput measures to determine systems capacity by observing when the number of waiting items is never zero and determining at what level, based on the system's presented workload, the items never wait. Utilization is a measure of the fraction of time that a particular resource is...
