3.3.6. Multi-level Priority Queue Scheduler

• A more complex scheme is often used to shift the behavior of the Round Robin Scheduler slightly in favor of short, interactive processes like the Shortest Job Next Scheduler.
• New processes begin in the highest priority queue.
• A process is rewarded by being moved to a higher priority queue if it voluntarily blocks for I/O before its time quantum expires. Similarly processes that are preemptively removed are penalized by being put in a lower priority queue.
• Queues with a lower priority use a longer time quantum.
• Higher priority queues must be empty before processes from lower priority queues are allowed to run. Thus, it is possible for starvation to occur.