FIFO simply queues processes in the order that they arrive in the ready queue. Using this algorithm the cache behaves in the same way as a FIFO queue. Another method allows the concurrent access of multiple processes to the same priority queue. The root node is inserted into the priority queue. Messages placed onto the queue are stored until the recipient retrieves them. The messages goes to a temporary storage transmission queue associated with a channel. The mailbox is modeled as a FIFO message queue. An application then registers a software routine that "listens" for messages placed onto the queue. There is also a stack that holds operators not yet added to the output queue. A message is placed on a remote queue. Thus each processor holds a representative part of the global priority queue. Each processor has its own local memory and a local (sequential) priority queue. The elements of the global (parallel) priority queue are distributed across all processors. The PRINT command adds or removes files in the print queue. This is often done via a stack (LIFO) or queue (FIFO).