The facets and the process of tuning an operating system through adjustment of the scheduler parameter settings to attain the most effective use of the operating system at a particular installation are described. Many modern computers are delivered with default installation parameters in their operating system so that each installation can make important efficiency decisions, such as the devices to be used for system program residence and scheduling options, in accordance with the properties of its workload. Judicious setting of these can be a major factor in good performance. The model system considered in this study is based upon the Control Data Corporation``s (CDC) CYBER 73-18 Computer System at the KIST Computer Center with SCOPE 3.4 operating system. The tuning procedure described here consist of a number of step which are used to select an appropriate set of scheduler parameters for a running system and aimed at producing a balanced system with a short turn-around time for batch jobs with minimal impact on the response time of interactive job. The technique used is based on both analytical method and simulation results.