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CPU scheduling is a crucial aspect of operating systems that determines the order in which processes are executed on the central processing unit (CPU). Two important metrics used to evaluate the efficiency of CPU scheduling algorithms are Turn Around Time (TAT) and Waiting Time (WT). Understanding the difference between these two metrics can provide insights into the performance and responsiveness of a CPU scheduling algorithm.
Turn Around Time (TAT)
Turn Around Time (TAT) is the total time taken for a process to complete its execution from the moment it enters the system until it finishes. It includes both the time the process spends executing on the CPU and the time it spends waiting for CPU time. TAT is measured from the start of the process to its completion and is often used to evaluate the overall efficiency of a scheduling algorithm. A shorter TAT indicates faster completion of processes and better system performance.
Impacts of TAT
Turn Around Time (TAT) is an important metric to indicate the performance of processes. Following are the some of the important points to consider for TAT.
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Calculation − TAT is calculated as the difference between the completion time and the arrival time of a process. It measures the overall time a process spends in the system, including both execution and waiting time.
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Importance − TAT provides a comprehensive measure of the process”s total turnaround time in the system. It helps assess the overall efficiency and performance of a CPU scheduling algorithm. A shorter TAT indicates faster completion of processes and better system performance.
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Impact − A shorter TAT implies that processes spend less time in the system, which leads to better resource utilization, improved responsiveness, and increased throughput. Minimizing TAT is crucial for meeting performance targets and ensuring efficient execution of processes.
Waiting Time (WT)
Waiting Time (WT) refers to the total amount of time a process spends waiting in the ready queue before it can be executed on the CPU. It is the time interval between the process”s arrival in the ready queue and the start of its execution. WT measures the extent to which processes have to wait for CPU time and is a crucial factor in assessing the efficiency of a CPU scheduling algorithm. Minimizing waiting time is desirable as it improves system responsiveness and reduces idle time for processes.
Impacts of TAT
Turn Around Time (TAT) is an important metric to indicate the scheduling of processes. Following are the some of the important points to consider for WT.
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Calculation − WT is calculated as the difference between the start time of execution and the arrival time of a process. It focuses solely on the waiting time component and does not include the execution time.
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Importance − WT reflects the waiting experience of individual processes in the ready queue. It provides insights into process responsiveness and the efficiency of a CPU scheduling algorithm.
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Impact − Reducing waiting time (WT) is crucial for improving system responsiveness, reducing process idle time, and enhancing overall performance. Minimizing WT ensures efficient utilization of the CPU and improves the user experience by reducing process delays and improving system throughput.
Difference between Turn Around Time (TAT) and Waiting Time (WT) in CPU Scheduling
The following table highlights the major differences between TAT and WT in CPU scheduling −
| S.N. | Criteria | Turn Around Time (TAT) | Waiting Time (WT) |
|---|---|---|---|
| 1 | Definition | The total time taken for a process to complete its execution | The total time a process spends waiting in the ready queue |
| 2 | Calculation | Completion time − Arrival time | Start time of execution − Arrival time |
| 3 | Inclusion | Includes both waiting time and execution time | Focuses solely on waiting time in the ready queue |
| 4 | Evaluation | Assesses the overall efficiency and performance of a scheduling algorithm | Reflects waiting experience and process responsiveness |
| 5 | Impact | Provides a comprehensive measure of process turnaround time | Directly affects system responsiveness and reduces idle time |
| 6 | Importance | Critical for evaluating the efficiency and performance of a scheduling algorithm | Crucial for improving system responsiveness and reducing waiting time |
| 7 | Optimization | Lower TAT indicates faster execution and better system performance | Minimizing WT improves system responsiveness and resource utilization |
| 8 | Measurement | Measured from the process arrival to completion | Measured from the process arrival to the start of execution |
| 9 | Purpose | Evaluates the efficiency of a scheduling algorithm as a whole | Focuses on individual process waiting times in the ready queue |
Conclusion
Understanding the differences between Turn Around Time (TAT) and Waiting Time (WT) is crucial in evaluating the efficiency and performance of a CPU scheduling algorithm. While TAT provides a comprehensive measure of the process”s total turnaround time, including waiting time and execution time, WT specifically focuses on the time a process spends waiting in the ready queue. By considering both metrics, system designers and schedulers can make informed decisions to optimize CPU scheduling algorithms, improve system responsiveness, and enhance overall performance.
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