Q2. Explain the Scheduling Criteria.
Ans. The following decides the scheduling criteria:
- CPU Utilization
We want to keep the CPU as busy as possible. Conceptually, CPU utilization can range from 0 to 100 percent. In a real system, it should range from 40 percent (for a lightly loaded system) to 90 percent (for heavily used system).
If the CPU is busy executing processes, then work is being done. One measure of work is the number of processes that are completely for time unit, called throughput. For long processes, this rate may be one process per hour, for short transaction, it may be 10 processes per second.
- Turnaround Time
From the point of view of a particular process, the important criterion is how long it takes to execute that process. The interval from the time of submission of a process to the time of completion is the turnaround time. Turnaround time is the sum of the periods spent waiting to get into memory, waiting in the ready queue, executing on the CPU, and doing input/output.
- Waiting Time
The CPU scheduling algorithm does not affect the amount of time during which a process executes or does input/output; it affects only the amount of time that a process sends waiting in the ready queue. Waiting Time is the sum of the periods spends waiting in the ready queue.
- Response Time
Often, a process can produce some output fairly early and can continue computing new results while previous results are being output to the user. Thus, another measure is the time from the submission of a request until the first response is produced. This measure, called response time, is the time it takes to start responding, not the time it takes to output the response.