The Highest Response Ratio Next (HRRN) is a CPU scheduling algorithm that prioritizes processes based on their expected waiting time. The HRRN algorithm calculates the response ratio of each process, which is defined as the ratio of the waiting time plus the execution time to the execution time. The process with the highest response ratio is selected to run next.
The HRRN algorithm operates as follows:
Initialization: When a process arrives in the system, it is placed in the ready queue, and its waiting time is set to zero. The response ratio is not calculated until the process has waited for some time.
Calculation of Response Ratio: The response ratio of a process is calculated using the following formula:
Response Ratio = (Waiting time + Execution time) / Execution time
The waiting time of a process is calculated as the time it has spent waiting in the ready queue. The execution time is the amount of time required for the process to complete its execution.
Selection of Next Process: The process with the highest response ratio is selected to run next. If two or more processes have the same response ratio, the process that arrived first is selected.
Updating of Waiting Time: The waiting time of the remaining processes in the ready queue is updated after each process is executed. The waiting time of a process is increased by the amount of time that has passed since its arrival in the system.
The HRRN algorithm provides good performance in terms of average waiting time and turnaround time, making it suitable for systems that require a high degree of fairness and responsiveness.
Example:
Consider a system with three processes, P1, P2, and P3, with the following attributes:
Process Arrival time Execution time P1 0 10 P2 2 5 P3 4 20
The following table shows the waiting time, response ratio, and the order in which the processes are executed using the HRRN algorithm:
Process Arrival time Execution time Waiting time Response Ratio P1 0 10 0 (0+10)/10 = 1 P2 2 5 0 (0+5)/5 = 1 P3 4 20 0 (0+20)/20 = 1
The processes are executed in the following order: P1, P2, P3.
At the end of the first time quantum, P1 has completed its execution, and P2 and P3 have waiting times of 10 and 14, respectively. The response ratios are calculated as follows:
Process Arrival time Execution time Waiting time Response Ratio P2 2 5 10 (10+5)/5 = 3 P3 4 20 14 (14+20)/20 = 2.4
The process with the highest response ratio, P2, is executed next. At the end of its execution, the waiting time of P3 is increased to 19, and its response ratio becomes (19+20)/20 = 1.95. P3 is executed next and completes its execution.
In this example, the HRRN algorithm provides good performance by executing the processes in a fair and responsive manner. The average waiting time and turnaround time are both minimized, making HRRN a suitable choice for systems that require high levels of fairness and responsiveness.
In conclusion, the HRRN algorithm is a CPU scheduling algorithm that prioritizes processes based on their expected waiting time. It calculates the response ratio of each process and selects the process with the highest response ratio to run next. The HRRN algorithm provides good performance in terms of average waiting time and turnaround time, making it a suitable choice for systems that require a high degree of fairness and responsiveness. This algorithm is especially useful in environments where there are a large number of interactive processes and background processes, as it ensures that the interactive processes receive adequate attention while the background processes are not neglected. Additionally, HRRN has the ability to adapt to changes in the system, making it an efficient scheduling algorithm for dynamic environments.
