Question 148: If shortest job first policy is used without pre-emption, what would be the average waiting time?
Options:
- 2
- 3
- 4
- 5
Solution: The correct answer is the third one. Average waiting time is (0 + 6 + 3 + 7)/4 = 4
Q70: Starvation in priority based scheduling
Question 70: In priority based scheduling, what is the solution to starvation?
- Starvation can be controlled by setting priorities appropriately.
- Fairness
- Aging
- Starvation can’t be stopped.
Solution: Aging refers to the technique of increasing the priority of the processes that wait in the ready queue for a long time. The correct answer is C.
Q22: Scheduling goal for batch systems
Question #22: Which of the following is not a scheduling goal for batch systems?
Options:
- Throughput
- CPU Utilization
- Response Time
- Turnaround Time
Solution:
Response time means getting the response to requests quickly, this is a concern for interactive systems, or game/video playing applications. Batch systems concern with keeping the system busy and fully utilized at all times. Hence, the correct answer is option 3, response time.
Q2: Shortest Remaining Time First
An operating system uses Shortest Remaining Time first (SRT) process scheduling algorithm. Consider the arrival times & execution times for the following processes:
Process Execution time Arrival time
P1 20 0
P2 25 15
P3 10 30
P4 15 45
Question #2: What is the total waiting time for process P2?
- 5
- 0
- 10
- 15
Solution: Following will be the timeline based on the SRT algorithm.
|—-P1—-|—-P1—-|—-P2—-|—-P3—-|—-P2—-|—-P2—-|—-P4—-|
0 15 20 30 40 45 55 70
P2 entered into the system at 15 and finished off at 55. The total time it stayed in the system is 55-15 = 40 and its execution time is 25. Hence, it waited for a total of 40-25 = 15 time units. Hence option 4th is the correct one.
Bytes of the day 