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Round Robin Scheduling Algorithm

In this tutorial, we are going to learn about the most efficient CPU Process Scheduling Algorithm named Round Robin CPU Process Scheduling. This algorithm is very special because it is going to remove all the Flaws which we have detected in the previous CPU Process Scheduling Algorithms.

There is a lot of popularity for this Round Robin CPU Scheduling is because Round Robin works only in Pre Emptive state. This makes it very reliable.

Important Abbreviations

  1. CPU - - - > Central Processing Unit
  2. AT - - - > Arrival Time
  3. BT - - - > Burst Time
  4. WT - - - > Waiting Time
  5. TAT - - - > Turn Around Time
  6. CT - - - > Completion Time
  7. FIFO - - - > First In First Out
  8. TQ - - - > Time Quantum

Round Robin CPU Scheduling

Round Robin CPU Scheduling is the most important CPU Scheduling Algorithm which is ever used in the history of CPU Scheduling Algorithms. Round Robin CPU Scheduling uses Time Quantum (TQ). The Time Quantum is something which is removed from the Burst Time and lets the chunk of process to be completed.

Time Sharing is the main emphasis of the algorithm. Each step of this algorithm is carried out cyclically. The system defines a specific time slice, known as a time quantum.

First, the processes which are eligible to enter the ready queue enter the ready queue. After entering the first process in Ready Queue is executed for a Time Quantum chunk of time. After execution is complete, the process is removed from the ready queue. Even now the process requires some time to complete its execution, then the process is added to Ready Queue.

The Ready Queue does not hold processes which already present in the Ready Queue. The Ready Queue is designed in such a manner that it does not hold non unique processes. By holding same processes Redundancy of the processes increases.

After, the process execution is complete, the Ready Queue does not take the completed process for holding.

os Round Robin Scheduling Algorithm


The Advantages of Round Robin CPU Scheduling are:

  1. A fair amount of CPU is allocated to each job.
  2. Because it doesn't depend on the burst time, it can truly be implemented in the system.
  3. It is not affected by the convoy effect or the starvation problem as occurred in First Come First Serve CPU Scheduling Algorithm.


The Disadvantages of Round Robin CPU Scheduling are:

  1. Low Operating System slicing times will result in decreased CPU output.
  2. Round Robin CPU Scheduling approach takes longer to swap contexts.
  3. Time quantum has a significant impact on its performance.
  4. The procedures cannot have priorities established.


Assume Time Quantum TQ = 5

Ready Queue:

Gantt chart:

os Round Robin Scheduling Algorithm

Average Completion Time

Average Waiting Time

Average Turn Around Time

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