Multilevel queue

Multi-level queueing, used at least since the late 1950s/early 1960s, is a queue with a predefined number of levels. Unlike the multilevel feedback queue, items gets assigned to a particular level at insert (using some predefined algorithm), and thus cannot be moved to another level. Items get removed from the queue by removing all items from a level, and then moving to the next. If an item is added to a level above, the "fetching" restarts from there. Each level of the queue is free to use its own scheduling, thus adding greater flexibility than merely having multiple levels in a queue.

Process Scheduling

Multi-level queue scheduling algorithm is used in scenarios where the processes can be classified into groups based on property like process type, CPU time, IO access, memory size, etc. One general classification of the processes is foreground processess and background processes. In multi-level queue scheduling algorithm, there will be 'n' number of queues, where 'n' is the number of groups the processes are classified into. Each queue will be assigned a priority and will have its own scheduling algorithm like RR [1] or [[2]]. For the process in a queue to execuete, all the queues of priority higher than it should be empty, meaning the process in those high priority queues should have completed its execution.