  Minimizing waiting time for tasks waiting in the queue for execution is one
of the important scheduling cri-teria which took a wide area in scheduling
preemptive tasks. In this paper we present Changeable Time Quan-tum (CTQ)
approach combined with the round-robin algorithm, we try to adjust the time
quantum according to the burst times of the tasks in the ready queue. There are
two important benefits of using (CTQ) approach: minimizing the average waiting
time of the tasks, consequently minimizing the average turnaround time, and
keeping the number of context switches as low as possible, consequently
minimizing the scheduling overhead. In this paper, we consider the scheduling
problem for preemptive tasks, where the time costs of these tasks are known a
priori. Our experimental results demonstrate that CTQ can provide much lower
scheduling overhead and better scheduling criteria.
