Alternative scheduling policies
A selection function determines which among the ready processes is next selected for execution Selection functions are based on one or more of these items:
1) w - time spent in system so far, waiting and executing.
2) e - time spent on execution so far.
3) s - total service time required by the process.
4) resources required by the process
When to apply the selection function is dependent on whether a preemptive or non-preemptive scheduling is used.