What is Priority Scheduling?

Priority Scheduling is a method of scheduling processes that is based on priority. In this algorithm, the scheduler selects the tasks to work as per the priority.

The processes with higher priority should be carried out first, whereas jobs with equal priorities are carried out on a round-robin or FCFS basis. Priority depends upon memory requirements, time requirements, etc.

Characteristics of Priority Scheduling

  • A CPU algorithm that schedules processes based on priority.
  • It used in Operating systems for performing batch processes.
  • If two jobs having the same priority are READY, it works on a FIRST COME, FIRST SERVED basis.
  • In priority scheduling, a number is assigned to each process that indicates its priority level.
  • Lower the number, higher is the priority.
  • In this type of scheduling algorithm, if a newer process arrives, that is having a higher priority than the currently running process, then the currently running process is preempted.

Advantages

  • Easy to use scheduling method
  • Processes are executed on the basis of priority so high priority does not need to wait for long which saves time
  • This method provides a good mechanism where the relative important of each process may be precisely defined.
  • Suitable for applications with fluctuating time and resource requirements.

Disadvantages

  • If the system eventually crashes, all low priority processes get lost.
  • If high priority processes take lots of CPU time, then the lower priority processes may starve and will be postponed for an indefinite time.
  • This scheduling algorithm may leave some low priority processes waiting indefinitely.
  • A process will be blocked when it is ready to run but has to wait for the CPU because some other process is running currently.
  • If a new higher priority process keeps on coming in the ready queue, then the process which is in the waiting state may need to wait for a long duration of time.

Algorithm

  • First input the processes with their arrival time, burst time and priority.
  • First process will schedule, which have the lowest arrival time, if two or more processes will have lowest arrival time, then whoever has higher priority will schedule first.
  • Now further processes will be schedule according to the arrival time and priority of the process. (Here we are assuming that lower the priority number having higher priority). If two process priority are same then sort according to process number.
    • Note: In the question, They will clearly mention, which number will have higher priority and which number will have lower priority.
  • Once all the processes have been arrived, we can schedule them based on their priority.
Simulate