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.