Definition
Highest Response Ratio Next (HRRN)
Highest Response Ratio Next (HRRN) selects the process with the highest response ratio:
where
is the waiting time and is the estimated service time.
Properties
Selection
The process with maximum
is chosen.
Non-Preemptive
Once running, a process continues until it terminates or blocks for I/O.
Starvation Freedom
Unlike SPN, HRRN prevents starvation. As
increases, even long processes eventually gain the highest ratio.
Efficiency
Favours shorter processes (small
) while gradually increasing priority of longer-waiting processes.
Overhead
Requires estimation of service times, similar to SPN.