When a process first enters the system, it is placed in RQ$0.$ After its first preemption, when it returns to the Ready state, it is placed in RQ$1($the highest priority queue$).$ Each subsequent time that it is preempted, it is demoted to the next low$-$priority queue. Within each queue, except the lowest$-$priority queue, a simple FCFS mechanism is used. Once in the lowest$-$priority queue, a process cannot go lower; but is returned to this queue repeatedly until it completes execution. Thus, this queue is treated in a round$-$robin fashion.