Questions and Answers
Which type of process spends more time doing I/O than computations and has many short CPU bursts?
I/O-bound process
What is the main concern when it comes to CPU burst distribution?
CPU utilization
Which scheduler selects which process should be executed next and allocated the CPU?
Short-term scheduler
Which scheduler selects which processes should be brought into the ready queue?
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Which scheduler controls the degree of multiprogramming?
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Which type of process spends more time doing computations and has few very long CPU bursts?
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Which scheduler is invoked frequently and must be fast?
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Which scheduler is invoked infrequently and may be slow?
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What is the objective of the long-term scheduler?
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What is the objective of the short-term scheduler?
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Which scheduling algorithm is considered fair but has a poor average waiting time?
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Which scheduling algorithm is not fair and has a poor average waiting time?
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Which scheduling algorithm minimizes the average waiting time assuming accurate prediction of the next CPU burst length, but can lead to starvation?
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Which scheduling algorithm is an approximation of SJF and uses multiple queues?
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In SJF scheduling, what is the average waiting time for the following burst times: P1: 3, P2: 16, P3: 9, P4: 0?
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In preemptive SJF scheduling with varying arrival times, what is the average waiting time for the following burst times and arrival times: P1: 1 (arrival: 0), P2: 5 (arrival: 1), P3: 2 (arrival: 2), P4: 4 (arrival: 3)?
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In priority scheduling, which process will be executed first if the priority numbers are as follows: P1: 3, P2: 1, P3: 4, P4: 5, P5: 2?
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In round robin scheduling with a time quantum of 4, what is the average waiting time for the following burst times: P1: 24, P2: 3, P3: 3?
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In round robin scheduling, if there are 4 processes and the time quantum is 5, how many time units will each process get at most?
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In round robin scheduling, what is the maximum waiting time for a process if there are 5 processes and the time quantum is 10?
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Which process scheduling algorithm aims to keep the CPU as busy as possible?
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What is the waiting time for process P2 in the FCFS scheduling algorithm if the process burst times are P1=24, P2=3, P3=3 and the processes arrive in the order P1, P2, P3?
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Which scheduling algorithm is optimal and gives the minimum average waiting time for a given set of processes?
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What is the context-switch time in an operating system?
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Which scheduling decision is nonpreemptive?
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What is the formula for calculating waiting time in nonpreemptive scheduling algorithms?
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What is the formula for calculating turnaround time in preemptive scheduling algorithms?
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What is the goal of CPU scheduling?
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What is the average waiting time for the FCFS scheduling algorithm if the processes arrive in the order P2, P3, P1 and the process burst times are P1=24, P2=3, P3=3?
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Which scheduling algorithm may result in the convoy effect?
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Which type of process spends more time doing computations and has few very long CPU bursts?
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Which scheduler is invoked frequently and must be fast?
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What is the formula for calculating turnaround time in preemptive scheduling algorithms?
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Which process scheduling algorithm aims to keep the CPU as busy as possible?
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What is the formula for calculating waiting time in nonpreemptive scheduling algorithms?
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Which scheduling algorithm minimizes the average waiting time assuming accurate prediction of the next CPU burst length, but can lead to starvation?
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Which scheduler controls the degree of multiprogramming?
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Which scheduling algorithm is considered fair but has a poor average waiting time?
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What is the average waiting time for the FCFS scheduling algorithm if the processes arrive in the order P2, P3, P1 and the process burst times are P1=24, P2=3, P3=3?
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What is the average waiting time for the following burst times in SJF scheduling: P1: 3, P2: 16, P3: 9, P4: 0?
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In round robin scheduling with a time quantum of 4, what is the average waiting time for the following burst times: P1: 24, P2: 3, P3: 3?
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Study Notes
Process Scheduling
- I/O-bound processes spend more time doing I/O than computations and have many short CPU bursts.
- CPU-bound processes spend more time doing computations and have few very long CPU bursts.
Schedulers
- Short-term scheduler selects which process should be executed next and allocated the CPU.
- Long-term scheduler selects which processes should be brought into the ready queue.
- Medium-term scheduler controls the degree of multiprogramming.
Scheduling Algorithms
- Short-term scheduler is invoked frequently and must be fast.
- Long-term scheduler is invoked infrequently and may be slow.
- The objective of the long-term scheduler is to control the degree of multiprogramming.
- The objective of the short-term scheduler is to select which process should be executed next.
Scheduling Algorithms' Properties
- First Come First Served (FCFS) is not optimal and can result in convoy effect.
- Shortest Job First (SJF) minimizes the average waiting time assuming accurate prediction of the next CPU burst length, but can lead to starvation.
- Priority scheduling is not fair and has a poor average waiting time.
- Round Robin (RR) is an approximation of SJF and uses multiple queues.
- Multilevel Feedback Queue (MFQ) aims to keep the CPU as busy as possible.
Calculating Waiting Time and Turnaround Time
- The formula for calculating waiting time in nonpreemptive scheduling algorithms is: Waiting Time = Burst Time of Previous Process.
- The formula for calculating turnaround time in preemptive scheduling algorithms is: Turnaround Time = Burst Time + Waiting Time.
Scheduling Goals
- The goal of CPU scheduling is to minimize the average waiting time.
Specific Scheduling Scenarios
- In SJF scheduling, the average waiting time for burst times P1: 3, P2: 16, P3: 9, P4: 0 is 11.
- In preemptive SJF scheduling with varying arrival times, the average waiting time for burst times P1: 1 (arrival: 0), P2: 5 (arrival: 1), P3: 2 (arrival: 2), P4: 4 (arrival: 3) is 4.
- In priority scheduling, the process with the highest priority number will be executed first.
- In round robin scheduling with a time quantum of 4, the average waiting time for burst times P1: 24, P2: 3, P3: 3 is 10.
- In round robin scheduling, if there are 4 processes and the time quantum is 5, each process will get at most 5 time units.
- In round robin scheduling, the maximum waiting time for a process if there are 5 processes and the time quantum is 10 is 40.
- The waiting time for process P2 in the FCFS scheduling algorithm if the process burst times are P1=24, P2=3, P3=3 and the processes arrive in the order P1, P2, P3 is 27.
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