1Which component of the Operating System is responsible for selecting a process from the ready queue and allocating the CPU to it?
A.Dispatcher
B.Interrupt Handler
C.Job Scheduler
D.CPU Scheduler
Correct Answer: CPU Scheduler
Explanation:
The CPU scheduler (or short-term scheduler) selects a process from the processes in memory that are ready to execute and allocates the CPU to that process.
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2The module that gives control of the CPU to the process selected by the short-term scheduler is known as:
A.Interrupt Service Routine
B.Dispatcher
C.Allocator
D.Scheduler
Correct Answer: Dispatcher
Explanation:
The dispatcher involves switching context, switching to user mode, and jumping to the proper location in the user program to restart that program.
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3What is 'Dispatch Latency'?
A.The time it takes for a process to complete execution
B.The time it takes for the dispatcher to stop one process and start another
C.The time taken by the CPU to execute an instruction
D.The time a process waits in the ready queue
Correct Answer: The time it takes for the dispatcher to stop one process and start another
Explanation:
Dispatch latency is the overhead time required for the dispatcher to stop the currently running process and start the execution of the newly selected process.
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4In which of the following situations is CPU scheduling decision mandatory (non-preemptive)?
A.When a process terminates
B.When a process switches from running to ready state
C.When a process switches from waiting to ready state
D.When a process switches from ready to running state
Correct Answer: When a process terminates
Explanation:
Non-preemptive scheduling occurs when a process keeps the CPU until it releases it, either by terminating or by switching to the waiting state.
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5Which scheduling algorithm results in the 'Convoy Effect'?
A.Round Robin
B.First-Come, First-Served
C.Shortest Job First
D.Priority Scheduling
Correct Answer: First-Come, First-Served
Explanation:
The Convoy Effect occurs in FCFS when short processes wait behind a long process, lowering CPU and device utilization.
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6What is the primary objective of the Shortest Job First (SJF) scheduling algorithm?
A.To maximize throughput
B.To minimize response time
C.To minimize average waiting time
D.To ensure fairness
Correct Answer: To minimize average waiting time
Explanation:
SJF is provably optimal in that it gives the minimum average waiting time for a given set of processes.
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7Preemptive Shortest Job First scheduling is also known as:
A.Shortest Remaining Time First
B.Multilevel Queue Scheduling
C.Preemptive Priority Scheduling
D.Round Robin
Correct Answer: Shortest Remaining Time First
Explanation:
If a new process arrives with a shorter CPU burst than what is left of the current executing process, the current process is preempted. This is SRTF.
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8In Round Robin scheduling, if the time quantum is extremely large, the algorithm degenerates into which scheduling policy?
A.Priority Scheduling
B.Shortest Job First
C.First-Come, First-Served
D.Multilevel Feedback Queue
Correct Answer: First-Come, First-Served
Explanation:
If the time quantum is very large, every process finishes its CPU burst without interruption, effectively making it FCFS.
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9What is the major drawback of Priority Scheduling?
A.Starvation
B.Deadlock
C.High overhead
D.Low throughput
Correct Answer: Starvation
Explanation:
Starvation (or indefinite blocking) occurs when low-priority processes are left waiting indefinitely because higher-priority processes keep arriving.
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10Which technique is used to solve the problem of starvation in Priority Scheduling?
A.Swapping
B.Paging
C.Context Switching
D.Aging
Correct Answer: Aging
Explanation:
Aging involves gradually increasing the priority of processes that wait in the system for a long time to ensure they eventually execute.
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11Which scheduling criteria refers to the number of processes that complete their execution per time unit?
A.Turnaround time
B.Throughput
C.CPU utilization
D.Response time
Correct Answer: Throughput
Explanation:
Throughput is the measure of work done, defined as the number of processes completed per unit of time.
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12Turnaround time is defined as:
A.The time a process spends waiting in the ready queue
B.The total time the CPU is busy
C.The time from submission to the first response
D.The time from submission of a process to the time of completion
Correct Answer: The time from submission of a process to the time of completion
Explanation:
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 I/O.
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13Which scheduling algorithm is designed specifically for time-sharing systems?
A.Shortest Job First
B.Round Robin
C.First-Come, First-Served
D.Non-preemptive Priority
Correct Answer: Round Robin
Explanation:
Round Robin allows the system to switch between processes quickly, giving users the illusion that they have the CPU to themselves, which is essential for time-sharing.
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14In Multilevel Feedback Queue scheduling, a process can:
A.Never be preempted
B.Only stay in one queue
C.Choose its own priority
D.Move between queues
Correct Answer: Move between queues
Explanation:
Unlike standard Multilevel Queue scheduling, Multilevel Feedback Queue scheduling allows processes to move between queues based on their CPU burst behavior.
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15If a process is I/O bound, in a Multilevel Feedback Queue, it should ideally be placed in:
A.The last queue in the system
B.A blocked queue permanently
C.A lower priority queue with a long time quantum
D.A higher priority queue with a short time quantum
Correct Answer: A higher priority queue with a short time quantum
Explanation:
I/O bound processes use the CPU briefly before waiting for I/O. Keeping them in high priority ensures quick initiation of I/O, improving device utilization.
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16What is 'Process Affinity' (or Processor Affinity) in multiprocessor scheduling?
A.Processes communicate via signals
B.A process creates a child process
C.Two processes share the same memory
D.A process prefers to run on the same processor it ran on previously
Correct Answer: A process prefers to run on the same processor it ran on previously
Explanation:
Processor affinity avoids the overhead of invalidating and repopulating caches by trying to keep a process on the same CPU.
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17Which of the following is NOT a characteristic of a Hard Real-Time System?
A.Deadlines are optional if system is busy
B.Guaranteed quality of service
C.Missing a deadline is a total system failure
D.Critical tasks must complete on time
Correct Answer: Deadlines are optional if system is busy
Explanation:
In Hard Real-Time systems, missing a deadline results in fundamental failure; deadlines are strictly mandatory.
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18Rate Monotonic Scheduling assigns priorities to tasks based on their:
A.CPU Burst time
B.Arrival time
C.Deadline
D.Period (frequency)
Correct Answer: Period (frequency)
Explanation:
Rate Monotonic Scheduling uses static priorities where tasks with shorter periods (higher frequency) get higher priorities.
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19Earliest Deadline First (EDF) scheduling assigns priorities:
A.Based on shortest burst
B.Statically based on period
C.Dynamically based on closeness to deadline
D.Randomly
Correct Answer: Dynamically based on closeness to deadline
Explanation:
EDF is a dynamic priority algorithm where the task with the closest deadline is assigned the highest priority.
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20In Thread Scheduling, the distinction between PCS (Process-Contention Scope) and SCS (System-Contention Scope) relies on:
A.The size of the thread
B.The programming language used
C.The amount of memory allocated
D.The level at which threads compete for CPU time
Correct Answer: The level at which threads compete for CPU time
Explanation:
PCS implies competition among threads of the same process (many-to-one or many-to-many), while SCS implies competition among all threads in the system (one-to-one).
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21The formula for calculating Waiting Time for a specific process is:
A.Response Time + Burst Time
B.Completion Time - Arrival Time
C.Turnaround Time - Burst Time
D.Burst Time + Arrival Time
Correct Answer: Turnaround Time - Burst Time
Explanation:
Waiting time is the total time a process spends waiting. Since Turnaround is (Waiting + Burst), Waiting = Turnaround - Burst.
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22Which scheduling algorithm is most difficult to implement because it requires predicting the future?
A.Round Robin
B.Multilevel Queue
C.FCFS
D.SJF
Correct Answer: SJF
Explanation:
SJF requires knowledge of the length of the next CPU burst, which is generally unknown and must be estimated.
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23In asymmetric multiprocessing:
A.Each processor has its own ready queue only
B.No processor controls another
C.All processors are peers
D.One processor (master) controls the system, others look to it or have predefined tasks
Correct Answer: One processor (master) controls the system, others look to it or have predefined tasks
Explanation:
Asymmetric multiprocessing follows a master-slave relationship where the master server handles data structures and scheduling.
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24Load balancing in multiprocessor systems involves:
A.Push migration and Pull migration
B.Reducing the number of processors
C.Disabling interrupts
D.Increasing the time quantum
Correct Answer: Push migration and Pull migration
Explanation:
Load balancing attempts to keep the workload evenly distributed. Push migration moves tasks from overloaded CPUs, and Pull migration takes tasks when a CPU is idle.
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25Which of the following is a criterion for 'Response Time'?
A.Time to output the first character
B.Time from submission to first response produced
C.Time spent in ready queue
D.Time to finish the whole job
Correct Answer: Time from submission to first response produced
Explanation:
In interactive systems, response time (time from request submission until the first response starts) is more critical than total turnaround time.
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26Under preemptive scheduling, when can the CPU be taken away from a process?
A.Only when the process requests I/O
B.When an interrupt occurs or a higher priority process arrives
C.Never
D.Only when the process terminates
Correct Answer: When an interrupt occurs or a higher priority process arrives
Explanation:
Preemptive scheduling allows the OS to interrupt a currently running process to allocate the CPU to another process.
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27What determines the efficiency of the Round Robin algorithm?
A.The memory size
B.The I/O speed
C.The number of processes
D.The size of the time quantum
Correct Answer: The size of the time quantum
Explanation:
If the quantum is too small, context switching overhead is high. If too large, it acts like FCFS. The quantum size is the critical tuning parameter.
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28In the context of scheduling, what is 'Little's Law' used for?
A.Detecting deadlocks
B.Determining average queue length based on arrival rate and average wait time
C.Estimating the next CPU burst
D.Assigning priorities
Correct Answer: Determining average queue length based on arrival rate and average wait time
Explanation:
Little's Law (N = lambda * W) relates the number of processes in the queue, arrival rate, and waiting time.
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29Which method is commonly used to predict the next CPU burst duration for SJF?
A.Random guessing
B.Fixed constant value
C.Exponential averaging of previous bursts
D.User input
Correct Answer: Exponential averaging of previous bursts
Explanation:
Exponential averaging weighs recent history more heavily to predict the next value based on past behavior.
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30What is 'Soft Affinity'?
A.The process runs only on the master processor
B.The process runs on any processor randomly
C.The OS guarantees the process runs on the same processor
D.The OS attempts to keep the process on the same processor but doesn't guarantee it
Correct Answer: The OS attempts to keep the process on the same processor but doesn't guarantee it
Explanation:
Soft affinity is a best-effort approach to keep a process on a specific CPU, usually to utilize cache, but migration is possible if necessary.
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31A system where the ready queue is partitioned into separate queues (e.g., foreground and background) with different scheduling algorithms is called:
A.FCFS
B.Round Robin
C.SJF
D.Multilevel Queue Scheduling
Correct Answer: Multilevel Queue Scheduling
Explanation:
Multilevel Queue scheduling partitions the ready queue, and processes are permanently assigned to one queue based on properties like memory size or process type.
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32Which priority applies in Windows scheduling when a thread is running in the kernel?
A.Idle priority
B.Variable priority
C.GUI priority
D.Real-time priority
Correct Answer: Variable priority
Explanation:
Windows uses a priority-based preemptive scheduling system; general threads usually fall into the variable class where priority can be boosted.
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33Pthread scheduling API allows specifying the scope of contention. What does PTHREAD_SCOPE_SYSTEM mean?
A.The thread is a kernel thread only
B.The thread competes only within the process
C.The thread competes with all threads in the system for CPU
D.The thread cannot be preempted
Correct Answer: The thread competes with all threads in the system for CPU
Explanation:
PTHREAD_SCOPE_SYSTEM maps the user thread directly to a kernel thread (one-to-one), competing for CPU time with all other processes.
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34In a real-time system, 'Interrupt Latency' refers to:
A.Time from interrupt arrival to the start of the execution of the ISR
B.Time waiting for the interrupt
C.Time to return from the ISR
D.Time to execute the ISR
Correct Answer: Time from interrupt arrival to the start of the execution of the ISR
Explanation:
Interrupt latency is the period of time from the arrival of an interrupt at the CPU to the start of the routine that services the interrupt.
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35Which scheduling algorithm ensures that no process waits more than (n-1) x q time units, where n is the number of processes and q is the time quantum?
A.FCFS
B.Priority
C.Round Robin
D.SJF
Correct Answer: Round Robin
Explanation:
In Round Robin, every process gets 1/n of the CPU time in chunks of at most q time units at once.
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36Cooperative scheduling is another name for:
A.Non-preemptive scheduling
B.Multiprocessor scheduling
C.Preemptive scheduling
D.Thread scheduling
Correct Answer: Non-preemptive scheduling
Explanation:
In cooperative (non-preemptive) scheduling, the process cooperates by voluntarily yielding control of the CPU.
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37Typically, a long-term scheduler executes:
A.When an interrupt occurs
B.Much less frequently than the short-term scheduler
C.Every few milliseconds
D.Only at system boot
Correct Answer: Much less frequently than the short-term scheduler
Explanation:
The long-term scheduler controls the degree of multiprogramming and runs infrequently (seconds or minutes) compared to the short-term scheduler (milliseconds).
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38Which of the following is true about 'Admission Control' in Real-Time Scheduling?
A.It admits all processes regardless of load
B.It admits a process only if the system can guarantee its deadline
C.It is used in FCFS
D.It ignores deadlines
Correct Answer: It admits a process only if the system can guarantee its deadline
Explanation:
Admission control prevents the system from being overloaded by rejecting tasks that cannot be completed within their deadlines.
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39In calculating average waiting time, what is the arrival time usually assumed to be if not specified?
A.0
B.1
C.10
D.Infinity
Correct Answer: 0
Explanation:
In standard textbook problems, unless specified otherwise, processes are often assumed to arrive at time t=0.
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40What is the main disadvantage of Multilevel Feedback Queue scheduling?
A.It is the most complex to implement and tune
B.It cannot handle I/O bound processes
C.It causes immediate deadlock
D.It does not support interactive users
Correct Answer: It is the most complex to implement and tune
Explanation:
It requires defining the number of queues, scheduling algorithms for each, methods for upgrading/demoting processes, and quantum sizes, making it complex.
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41What happens to the 'Context Switch' time?
A.It shortens the process execution
B.It is pure overhead
C.It is used for I/O
D.It is useful processing time
Correct Answer: It is pure overhead
Explanation:
The system does no useful work while switching contexts; it simply saves and restores state.
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42Conflict phase of dispatch latency typically involves:
A.Waiting for user input
B.Formatting the hard drive
C.Loading the new program from disk
D.Preemption of any process running in the kernel and release by low-priority process of resources
Correct Answer: Preemption of any process running in the kernel and release by low-priority process of resources
Explanation:
Before a high-priority real-time task can run, the kernel must resolve conflicts by preempting current kernel activities and releasing low-priority locks.
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43Which scheduling algorithm suffers from the problem of indefinite blocking?
A.Priority Scheduling
B.FIFO
C.Round Robin
D.Rate Monotonic
Correct Answer: Priority Scheduling
Explanation:
A low priority process might never get the CPU if high priority processes keep arriving (starvation).
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44In SMP (Symmetric Multiprocessing), where can a process run?
A.Only on CPU 0
B.On any available processor
C.On the I/O processor only
D.On the GPU only
Correct Answer: On any available processor
Explanation:
In SMP, all processors are peers, and a process (or thread) can generally run on any available CPU.
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45What is the 'Throughput' if 10 processes finish in 5 seconds?
A.5 processes/second
B.0.5 processes/second
C.2 processes/second
D.50 processes/second
Correct Answer: 2 processes/second
Explanation:
Throughput = Total processes / Total time = 10 / 5 = 2.
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46Typically, 'Foreground' processes in a Multilevel Queue system use which algorithm?
A.Random
B.SJF
C.Round Robin
D.FCFS
Correct Answer: Round Robin
Explanation:
Foreground processes are interactive, so they require low response time, which Round Robin provides.
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47Typically, 'Background' processes in a Multilevel Queue system use which algorithm?
A.Round Robin
B.Priority
C.FCFS
D.Real-time
Correct Answer: FCFS
Explanation:
Background processes (batch jobs) do not require user interaction, so FCFS is often used for its simplicity and low overhead.
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48Which type of thread scheduling allows the user-level thread library to schedule threads?
A.System-Contention Scope (SCS)
B.Hard Real-time
C.Process-Contention Scope (PCS)
D.Round Robin
Correct Answer: Process-Contention Scope (PCS)
Explanation:
In PCS, the thread library schedules user-level threads onto available LWPs (Lightweight Processes).
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49If a process has a CPU burst of 10ms and the time quantum is 20ms, what happens?
A.The process runs for 10ms, terminates/yields, and the context switches
B.The CPU idles for 10ms
C.The process is forced to run for 20ms
D.An error occurs
Correct Answer: The process runs for 10ms, terminates/yields, and the context switches
Explanation:
A process voluntarily releases the CPU if its burst is less than the quantum; it doesn't hold it for the full quantum.
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50Which concept describes the cycle of CPU execution and I/O wait?
A.Fetch-Decode-Execute Cycle
B.Boot Cycle
C.CPU-I/O Burst Cycle
D.Interrupt Cycle
Correct Answer: CPU-I/O Burst Cycle
Explanation:
Process execution consists of a cycle of CPU execution (CPU burst) and I/O wait (I/O burst).