Under preemptive scheduling, the highest priority task executes until it enters the waiting or dead states or a higher priority task comes into existence. The main advantage is that they ensure fairness to all jobs, regardless of its priority and also provide quick response time depending on the CPU time the job needs.The main disadvantage is that it provides indefinite postponement to process/task.
Under time slicing, a task executes for a predefined slice of time (quantum) and then reenters the pool of ready tasks. The scheduler then determines which task should execute next, based on priority and other factors. Advantages are that it is effective in a general-purpose, times-sharing system or transaction-processing system which provides fair treatment for all the processes. Its overhead on processor is low and provide good response time for short processes. Disadvantages are that care must be taken in choosing quantum value if it is too low then there would be a lot of context switching and if it is too high then it can behave as other algorithms.
