OS Process Scheduling Q & A #4

Question: What is Highest Response Ratio Next (HRN) Scheduling?


  • HRN is non-preemptive scheduling algorithm.

  • In Shortest Job First scheduling, priority is given to shortest job, which may sometimes indefinite blocking of longer job.

  • HRN Scheduling is used to correct this disadvantage of SJF.

  • For determining priority, not only the job's service time but the waiting time is also considered.

  • In this algorithm, dynamic priorities are used instead of fixed priorities.

  • Dynamic priorities in HRN are calculated as

    Priority = (waiting time + service time) / service time.

  • So shorter jobs get preference over longer processes because service time appears in the denominator.

  • Longer jobs that have been waiting for long period are also give favorable treatment because waiting time is considered in numerator.

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