Chapter 6

Question 1

What is CPU scheduling?

Answer 1

The process of selecting which ready process should be executed next by the CPU.

Question 2

What is the CPU–I/O burst cycle?

Answer 2

A process alternates between CPU bursts (execution) and I/O bursts (waiting).

Question 3

Why is CPU scheduling important?

Answer 3

To keep the CPU busy as much as possible, improving efficiency and responsiveness.

Question 4

What is a CPU burst?

Answer 4

The time a process spends using the CPU for computation.

Question 5

What is an I/O burst?

Answer 5

The time a process spends waiting for input/output operations to complete.

Question 6

What happens when a running process requests I/O?

Answer 6

It moves from the running state to the waiting state, and the CPU is assigned to another process.

Question 7

What are the three main types of schedulers?

Answer 7

Long-term (job), Short-term (CPU), and Medium-term (swap) schedulers.

Question 8

What does the long-term scheduler do?

Answer 8

It controls how many programs are loaded into memory at onc

Question 9

What does the short-term scheduler do?

Answer 9

Chooses which ready process runs next on the CPU.

Question 10

What does the medium-term scheduler do?

Answer 10

Temporarily removes processes from memory (swapping) to reduce load.

Question 11

What is a dispatcher?

Answer 11

A module that gives control of the CPU to the process selected by the short-term scheduler.

Question 12

What are the dispatcher’s functions?

Answer 12

Performs context switching, switches to user mode, and jumps to the proper location in the user program.

Question 13

What is dispatcher latency?

Answer 13

The time it takes the dispatcher to stop one process and start another.

Question 14

What is a scheduling mechanism?

Answer 14

The low-level implementation of process selection and switching.

Question 15

What is a scheduling policy?

Answer 15

The decision-making rule for choosing which process should run next.

Question 16

What is preemptive scheduling?

Answer 16

The CPU can be taken away from a process before it finishes its burst.

Question 17

What is non-preemptive scheduling?

Answer 17

Once a process gets the CPU, it cannot be taken away until it finishes or waits voluntarily.

Question 18

List five scheduling criteria.

Answer 18

CPU utilization, Throughput, Turnaround time, Waiting time, and Response time.

Question 19

What is CPU utilization?

Answer 19

The percentage of time the CPU is busy doing useful work.

Question 20

What is throughput?

Answer 20

The number of processes completed per unit of time.

Question 21

What is turnaround time?

Answer 21

The total time taken from process submission to completion.

Question 22

What is waiting time?

Answer 22

The total time a process spends waiting in the ready queue.

Question 23

What is response time?

Answer 23

The time from process submission until the first output or response.

Question 24

What is FCFS scheduling?

Answer 24

First-Come, First-Served; processes are executed in the order they arrive.

Question 25

Is FCFS preemptive or non-preemptive?

Answer 25

Non-preemptive.

Question 26

What is the main drawback of FCFS?

Answer 26

Convoy effect — short processes wait behind long ones.

Question 27

What is SJF scheduling?

Answer 27

Shortest Job First; selects the process with the shortest next CPU burst.

Question 28

Is SJF preemptive or non-preemptive?

Answer 28

It can be either; preemptive version is SRTF (Shortest Remaining Time First).

Question 29

Why is SJF optimal?

Answer 29

It provides the minimum average waiting time for a given set of processes.

Question 30

What is SRTF?

Answer 30

Shortest Remaining Time First; preemptive version of SJF where a new shorter job can preempt the current one.

Question 31

What is the disadvantage of SJF/SRTF?

Answer 31

Starvation of long processes if short ones keep arriving.

Question 32

What is Priority Scheduling?

Answer 32

Each process has a priority; CPU goes to the highest priority process.

Question 33

What is a problem with priority scheduling?

Answer 33

Starvation — low-priority processes may never execute.

Question 34

How can starvation be fixed in priority scheduling?

Answer 34

Using aging — gradually increasing the priority of waiting processes.

Question 35

What is Round Robin (RR) scheduling?

Answer 35

Each process gets a small time slice (quantum) and is preempted after that time expires.

Question 36

What is the key benefit of Round Robin?

Answer 36

Good response time for interactive users.

Question 37

What is the effect of a very large quantum in RR?

Answer 37

It behaves like FCFS scheduling.

Question 38

What is the effect of a very small quantum in RR?

Answer 38

Too many context switches cause high overhead.

Question 39

What is a multilevel queue?

Answer 39

A scheduling method where processes are divided into multiple queues based on priority or type.

Question 40

How does a multilevel queue scheduler work?

Answer 40

Each queue may use its own algorithm (e.g., RR for foreground, FCFS for background).

Question 41

What problem can occur in multilevel queues?

Answer 41

Starvation of lower-priority queues if upper queues dominate.

Question 42

What is a multilevel feedback queue?

Answer 42

A dynamic scheduling system where processes can move between queues based on behavior.

Question 43

What is the advantage of multilevel feedback queues?

Answer 43

It adapts to process behavior and prevents starvation.

Question 44

What is asymmetric multiprocessing?

Answer 44

One CPU controls all scheduling and I/O, while others only run user processes.

Question 45

What is symmetric multiprocessing (SMP)?

Answer 45

Each processor is self-scheduling and may use a common or private ready queue.

Question 46

What is processor affinity?

Answer 46

A tendency for a process to stay on the same CPU to improve cache performance.

Question 47

What are the two types of processor affinity?

Answer 47

Soft affinity (preferred CPU) and hard affinity (fixed CPU).

Question 48

What is load balancing?

Answer 48

Distributing processes evenly among CPUs to prevent some from being overloaded.

Question 49

What are the two types of load balancing?

Answer 49

Push migration (moves tasks from busy CPUs) and pull migration (idle CPUs steal tasks).

Question 50

What is context switching?

Answer 50

Saving the state of one process and loading the state of another during scheduling.

Question 51

How does preemption affect synchronization?

Answer 51

Preemptive scheduling can interrupt processes in critical sections, causing race conditions if not managed carefully.

Question 52

Which scheduling algorithm gives the best response time?

Answer 52

Round Robin with a properly chosen time quantum.

Question 53

Which scheduling algorithm minimizes average waiting time?

Answer 53

Shortest Job First (SJF).