3.8 Randomness

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3.8 Randomness

Just as important to modeling as the concept of independence is the concept of randomness of events. Randomness is a property of an event and its reoccurrence. If an event is random, it implies that there is not a pattern that can be mapped onto the events to determine when they will occur again. Randomness is difficult, if not impossible, to prove. The converse, however, can be shown-that is, that an event is not random. We can use the assertion that a pattern does not exist as a way of indicating that the past will not aid in defining the future of an event. A random sequence of trials is the realization of the property of independence defined in the previous section.

Randomness is a mathematical concept. In mathematics we think of random numbers coming from a random infinite source. In practice, there are finite sequences of available numbers, and once they are generated they now have a pattern. For example, if we roll the die, before we roll it we have no idea which number will occur; but after it is rolled there is only one outcome.

In a computer system, the events caused by external sources (e.g., user key strokes, remote calls to a server) can be viewed as random events. Thus, their occurrence cannot be predicted ahead of time nor can the future after the last occurrence. This concept becomes very important when we wish to analyze our computer systems using mathematical concepts.

More on the concept of randomness will be discussed when we look at random variables and their use in modeling computing systems as Markov chains and Markov processes in later chapters.



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Computer Systems Performance Evaluation and Prediction
Computer Systems Performance Evaluation and Prediction
ISBN: 1555582605
EAN: 2147483647
Year: 2002
Pages: 136

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