1. Operational Laws A large number of day-to-day problem in computer systems performance analysis can be solved by using some simple relationships that do not require any assumptions about distribution of service times or interarrival times. Several such relationships called operational laws were identified originally by Buzen (1976) and later extended by Denning and Buzen (1978). The word operational means directly measured. Thus, operationally testable assumptions are the assumptions that can be verified by measurements.

2. Notation WAccumulated waiting time TLength of an observation interval A k Number of arrivals observed C k Number of completions observed λ k Arrivals rate X k Throughput B k Busy time

3. Notation (cont’d) U k Utilization S k Service requirement per visit NCustomer population R k Residence time ZThink time of a terminal user V k Number of visits D k Service demand

4. Fundamental Laws The Utilization Law: Little’s Law:

5. Fundamental Laws (cont’d) The Response Time Law: The Forced Flow Law:

6. Additional Relationships

7. More about Little’s Law Accumulated Time in System; Average Number of Requests in System; Average System Residence Time;

8. More about Little’s Law (cont’d) N = X 0 · R