Operating Systems | Scheduling Algorithms: HRRN

Highest Response Ratio Next(HRRN)

Response ration of a process in ready state at a moment is the ratio of sum of service time (equal to burst time) required and waiting time till that moment to the burst time.

Among available processes on ready state ,a process with highest response ratio get allocated to CPU by a scheduler with HRRN algorithm. If response ratios are equal next priority will for one which is arrived first and even that also similar then next is for onw with lowest process ID.

Example: Calculate completion time, turn around time and waiting time for the following processes using non-preemptive HRRN algorithm?

Process AT BT
P1 0 4
P2 1 3
P3 1 1
P4 3 2


The sequences of allocation of process into CPU can be depicted as follows:

TAT = CT - AT & WT = TAT - BT

Process Number AT BT CT TAT WT
1 0 4 10 10 6
2 1 3 8 7 4
3 1 1 3 2 1
4 3 2 9 6 4

The HRRN algorithm not only favors the shortest job with longer waiting time but also limits the waiting time and starvation on longer processes.