Process Scheduling Queues

Different states of processes use their individual queues to keep the number of processes, known as Process Scheduling Queues. Identical PCB of each process also exists in that queue.

 The OS maintains the following scheduling Queues.

  • Process queue: The process queue keeps a record of all those processes that exist in secondary memory.
  • Ready queue: The ready queue keeps a set of all processes that exist in the main memory and are ready to execute.
  • Wait queue: Those processes that are blocked by OS exist in the waiting queue. It is due to requesting a process for an I/O device or user input request.
  • Suspended Queue: It contains processes, temporarily kicked out of main memory.

OS maintains all PCBs of each process in their scheduling Queues. It uses different process scheduling algorithms to manage each queue.

Two-State Process Model

The state process model tells us whether the process is running or not.

State Description
Running When a process is created, then it enters into the system as a running state.
Not-Running Not running processes are kept in a waiting queue for their turn to execute. Dispatcher is used for this purpose.