1What is the primary role of an Operating System as a resource manager?
A.To arbitrate conflicting requests for resources and allocate them efficiently
B.To perform high-speed mathematical calculations
C.To compile source code into machine code
D.To provide a graphical user interface for applications
Correct Answer: To arbitrate conflicting requests for resources and allocate them efficiently
Explanation:
The OS acts as a resource manager that manages the CPU, memory, and I/O devices, arbitrating conflicting requests to ensure efficient system operation.
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2Which component of the Operating System resides in the main memory and interacts directly with the hardware?
A.Kernel
B.Compiler
C.Command Interpreter
D.Shell
Correct Answer: Kernel
Explanation:
The kernel is the core component of the OS that remains in memory and handles low-level hardware interactions.
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3In a Time-Sharing System, what is the primary mechanism used to switch the CPU between users?
A.Virtual Memory
B.First-Come, First-Served
C.Context Switching
D.Deadlock Avoidance
Correct Answer: Context Switching
Explanation:
Time-sharing systems use rapid context switching to create the illusion that multiple users are using the CPU simultaneously.
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4Which of the following characterizes a Hard Real-Time System?
A.Missing a deadline results in total system failure
B.It is used primarily for batch processing
C.Throughput is the only metric of importance
D.Deadlines are desirable but not mandatory
Correct Answer: Missing a deadline results in total system failure
Explanation:
In Hard Real-Time Systems (e.g., pacemaker, flight control), strict deadlines must be met; failure to do so is catastrophic.
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5What is the mode bit used for in modern processors?
A.To switch between 32-bit and 64-bit processing
B.To distinguish between User Mode and Kernel Mode
C.To flag a page fault
D.To indicate if the printer is ready
Correct Answer: To distinguish between User Mode and Kernel Mode
Explanation:
The hardware uses a mode bit (0 for kernel, 1 for user) to distinguish between executing sensitive OS instructions and standard user applications.
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6Which system call is used in UNIX/Linux to create a new process?
A.init()
B.create()
C.new()
D.fork()
Correct Answer: fork()
Explanation:
The fork() system call is used to create a new process, which is an exact copy of the calling process.
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7What information is stored in the Process Control Block (PCB)?
A.Process state, Program Counter, CPU registers, and scheduling info
B.The file system directory structure
C.The list of all users on the system
D.The source code of the program
Correct Answer: Process state, Program Counter, CPU registers, and scheduling info
Explanation:
The PCB is a data structure used by the OS to store all information specific to a process.
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8In the context of Process State transitions, when does a process move from Running to Ready?
A.When it creates a child process
B.When an interrupt (like a timer expiry) occurs
C.When it finishes execution
D.When it requests I/O
Correct Answer: When an interrupt (like a timer expiry) occurs
Explanation:
A process moves from Running to Ready when it is interrupted (preempted), usually due to a time quantum expiry in scheduling.
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9What is long-term scheduling responsible for?
A.Selecting which processes are brought into the ready queue from the job pool
B.Swapping processes in and out of memory
C.Selecting which process should be executed next by the CPU
D.Handling interrupts
Correct Answer: Selecting which processes are brought into the ready queue from the job pool
Explanation:
Long-term scheduling (Job Scheduler) controls the degree of multiprogramming by selecting jobs to enter the system.
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10If the Degree of Multiprogramming is too high, what phenomenon might occur?
A.Fragmentation
B.Thrashing
C.Starvation
D.Deadlock
Correct Answer: Thrashing
Explanation:
Thrashing occurs when the system spends more time paging (swapping pages in and out) than executing processes because too many processes are competing for limited memory.
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11Calculate the Turnaround Time () if the Completion Time () is 15ms and the Arrival Time () is 3ms.
A.18ms
B.12ms
C.5ms
D.45ms
Correct Answer: 12ms
Explanation:
Turnaround Time is calculated as . Therefore, .
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12Which scheduling algorithm suffers from the Convoy Effect?
A.Priority Scheduling
B.Shortest Job First (SJF)
C.Round Robin (RR)
D.First-Come, First-Served (FCFS)
Correct Answer: First-Come, First-Served (FCFS)
Explanation:
The Convoy Effect happens in FCFS when short processes get stuck waiting behind a long CPU-bound process.
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13In Shortest Job First (SJF) scheduling, what is the main difficulty in implementation?
A.It does not support multiprogramming
B.It leads to frequent context switches
C.It requires complex data structures
D.It is impossible to know the length of the next CPU burst in advance
Correct Answer: It is impossible to know the length of the next CPU burst in advance
Explanation:
SJF is optimal but difficult to implement because the OS cannot precisely predict the length of the next CPU burst for a process.
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14Which scheduling algorithm is designed specifically for Time-Sharing Systems?
A.Shortest Job First
B.First-Come, First-Served
C.Round Robin
D.Multilevel Queue
Correct Answer: Round Robin
Explanation:
Round Robin uses a time quantum to switch between processes, ensuring responsiveness for time-sharing systems.
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15In Priority Scheduling, what technique is used to solve the problem of Starvation?
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.
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16Consider three processes P1, P2, P3 with burst times 10, 5, and 8 respectively. In FCFS, if they arrive in order P1, P2, P3, what is the waiting time for P3?
A.15
B.0
C.10
D.23
Correct Answer: 15
Explanation:
P1 runs for 10 (0-10). P2 runs for 5 (10-15). P3 starts at 15. Since P3 arrived at 0, its waiting time is 15.
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17What is the definition of Throughput in CPU scheduling?
A.The number of processes that complete their execution per time unit
B.The percentage of time the CPU is busy
C.The amount of time a process spends waiting in the ready queue
D.The time from submission to completion
Correct Answer: The number of processes that complete their execution per time unit
Explanation:
Throughput measures the rate at which processes are completed.
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18In a Multilevel Feedback Queue, a process that uses too much CPU time is usually:
A.Moved to a higher priority queue
B.Terminated immediately
C.Left in the same queue
D.Moved to a lower priority queue
Correct Answer: Moved to a lower priority queue
Explanation:
Multilevel Feedback Queues punish CPU-bound processes by moving them to lower priority queues to allow interactive (I/O bound) processes to run.
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19Which type of memory fragmentation occurs when there is enough total free space to satisfy a request, but the available spaces are not contiguous?
A.Page Fault
B.Internal Fragmentation
C.Segmentation Fault
D.External Fragmentation
Correct Answer: External Fragmentation
Explanation:
External fragmentation happens when free memory is scattered in small blocks, making it impossible to allocate a large contiguous block.
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20In Paging, the physical memory is divided into fixed-sized blocks called:
A.Segments
B.Sectors
C.Pages
D.Frames
Correct Answer: Frames
Explanation:
Physical memory is divided into Frames, while logical memory is divided into Pages of the same size.
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21The mapping of a logical address to a physical address is done in hardware by the:
A.Translation Lookaside Buffer (TLB)
B.Memory Management Unit (MMU)
C.Direct Memory Access (DMA)
D.Arithmetic Logic Unit (ALU)
Correct Answer: Memory Management Unit (MMU)
Explanation:
The MMU is the hardware device responsible for run-time mapping from virtual to physical addresses.
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22If a logical address consists of a page number and an offset , the physical address is generated by:
A.Adding to the base register
B.Subtracting from the limit register
C.Using as an index into the page table to find frame , then combining with
D.Multiplying by the frame size
Correct Answer: Using as an index into the page table to find frame , then combining with
Explanation:
The page table maps page number to frame number . The offset is not changed, resulting in physical address .
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23What is the purpose of the Translation Lookaside Buffer (TLB)?
A.To cache recently used page-table entries to speed up address translation
B.To store dirty pages before writing to disk
C.To store the entire page table
D.To handle page faults
Correct Answer: To cache recently used page-table entries to speed up address translation
Explanation:
The TLB is a fast associative memory cache used to reduce the effective memory access time by storing recent translations.
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24What is Internal Fragmentation?
A.When memory is allocated in fixed-sized blocks and the process needs less than the allocated block size
B.When the page table becomes too large
C.When memory is scattered in non-contiguous blocks
D.When the hard disk is fragmented
Correct Answer: When memory is allocated in fixed-sized blocks and the process needs less than the allocated block size
Explanation:
Internal fragmentation occurs inside an allocated partition (like the last page of a process) when the data is smaller than the partition size.
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25Which page replacement algorithm suffers from Belady's Anomaly?
A.Optimal
B.LFU (Least Frequently Used)
C.LRU (Least Recently Used)
D.FIFO (First-In, First-Out)
Correct Answer: FIFO (First-In, First-Out)
Explanation:
Belady's Anomaly is the phenomenon where increasing the number of page frames results in an increase in page faults, occurring in FIFO.
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26What is the Optimal Page Replacement algorithm?
A.Replace the page with the lowest frequency count
B.Replace the page that has been in memory the longest
C.Replace the page that will not be used for the longest period of time
D.Replace the page that was used least recently
Correct Answer: Replace the page that will not be used for the longest period of time
Explanation:
The Optimal algorithm replaces the page that will not be used for the longest duration in the future. It requires future knowledge, so it is used mainly for comparison.
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27In Segmentation, a logical address consists of:
A.Base, Limit
B.Segment number, Offset
C.Frame number, Key
D.Page number, Offset
Correct Answer: Segment number, Offset
Explanation:
Segmentation views memory as a collection of segments, addressed by a tuple: .
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28Which bit in a page table entry indicates whether the page has been modified (written to)?
A.Valid/Invalid bit
B.Dirty (Modify) bit
C.Protection bit
D.Reference bit
Correct Answer: Dirty (Modify) bit
Explanation:
The Dirty bit is set when a page is written to. If set, the page must be written back to disk (swapped out) before being replaced.
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29What is a Race Condition?
A.When two processes try to print at the same time
B.A condition where a process runs faster than the CPU clock
C.A situation where multiple processes read and write shared data concurrently and the outcome depends on the order of execution
D.A scheduling algorithm for real-time systems
Correct Answer: A situation where multiple processes read and write shared data concurrently and the outcome depends on the order of execution
Explanation:
A race condition occurs when the final state of shared data depends on the specific timing or ordering of concurrent process execution.
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30The segment of code where a process accesses shared resources is called the:
A.Remainder Section
B.Critical Section
C.Entry Section
D.Exit Section
Correct Answer: Critical Section
Explanation:
The Critical Section is the part of the code where shared resources (variables, files, etc.) are accessed.
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31Which of the following is NOT a requirement for a solution to the Critical Section Problem?
A.Progress
B.Bounded Waiting
C.First-Come First-Served
D.Mutual Exclusion
Correct Answer: First-Come First-Served
Explanation:
The three requirements are Mutual Exclusion, Progress, and Bounded Waiting. FCFS is a scheduling policy, not a synchronization requirement.
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32What is a Semaphore?
A.A type of system call for I/O
B.A distinct memory segment
C.A hardware interrupt
D.An integer variable accessed only through two atomic operations: wait() and signal()
Correct Answer: An integer variable accessed only through two atomic operations: wait() and signal()
Explanation:
A semaphore is a synchronization tool (integer variable) used to manage concurrent processes via atomic operations.
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33If a semaphore is initialized to 1, and process P1 executes wait(S), what is the new value of ?
A.2
B.1
C.0
D.-1
Correct Answer: 0
Explanation:
The wait(S) operation decrements the value of the semaphore. If , it becomes 0 and the process enters the critical section.
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34What is a Binary Semaphore often called?
A.Mutex Lock
B.Counter
C.Monitor
D.Spinlock
Correct Answer: Mutex Lock
Explanation:
A binary semaphore takes values 0 and 1, providing Mutual Exclusion, hence the name Mutex.
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35In the Producer-Consumer problem using a bounded buffer, what happens if the buffer is full?
A.The system crashes
B.Data is overwritten
C.The Consumer blocks
D.The Producer blocks
Correct Answer: The Producer blocks
Explanation:
If the buffer is full, the Producer must wait (block) until the Consumer removes an item and creates space.
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36Which of the following is NOT a necessary condition for Deadlock to occur (Coffman conditions)?
A.Circular Wait
B.Preemption
C.Hold and Wait
D.Mutual Exclusion
Correct Answer: Preemption
Explanation:
The condition is No Preemption. If resources can be preempted (taken away), deadlocks can be broken.
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37The Banker's Algorithm is used for:
A.Deadlock Recovery
B.Deadlock Prevention
C.Deadlock Detection
D.Deadlock Avoidance
Correct Answer: Deadlock Avoidance
Explanation:
The Banker's Algorithm avoids deadlock by simulating resource allocation and checking if the system remains in a 'Safe State'.
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38What does the Circular Wait condition imply?
A.A set of processes exists such that waits for , waits for , ..., waits for
B.Processes are waiting in a circle for CPU time
C.The scheduler uses Round Robin
D.Memory is allocated in a circular buffer
Correct Answer: A set of processes exists such that waits for , waits for , ..., waits for
Explanation:
Circular wait describes a closed chain of processes where each process holds a resource that the next process in the chain needs.
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39Which Inter-process Communication (IPC) mechanism allows data to flow in only one direction?
A.Ordinary Pipe (Anonymous Pipe)
B.Socket
C.Shared Memory
D.Message Queue
Correct Answer: Ordinary Pipe (Anonymous Pipe)
Explanation:
Standard ordinary pipes are unidirectional (half-duplex). Data flows from the write-end to the read-end.
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40What is the Dining Philosophers Problem an example of?
A.CPU Scheduling efficiency
B.File System corruption
C.Synchronization and Deadlock issues
D.Memory Management issues
Correct Answer: Synchronization and Deadlock issues
Explanation:
It is a classic synchronization problem illustrating the challenges of allocating limited resources (forks) among concurrent processes (philosophers) without causing deadlock or starvation.
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41In a system with instances of a resource and processes, if , what can be said about Deadlock?
A.Deadlock will never occur
B.Deadlock is inevitable
C.Deadlock might occur depending on timing
D.The system is in an unsafe state
Correct Answer: Deadlock will never occur
Explanation:
This is a derived formula. If the total resources cover the worst-case scenario where every process holds resources plus one extra to finish one process, deadlock is impossible.
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42What is a Spinlock?
A.A type of deadlock
B.A hard disk mechanism
C.A lock where a thread loops (spins) while waiting for the lock to become available
D.A scheduling queue
Correct Answer: A lock where a thread loops (spins) while waiting for the lock to become available
Explanation:
Spinlocks cause the waiting process to busy-wait (loop) checking the lock condition, which wastes CPU cycles but avoids context switch overhead.
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43In the context of IPC, what does Message Passing involve?
A.Writing to a hard disk file
B.Two processes sharing a variable in memory
C.Using CPU registers directly
D.Using send() and receive() primitives
Correct Answer: Using send() and receive() primitives
Explanation:
Message passing allows processes to communicate without shared memory by explicitly sending and receiving messages.
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44What is the main advantage of Threads over Processes?
A.Context switching between threads is faster and they share resources
B.Threads are more secure
C.Threads cannot deadlock
D.Threads have their own memory space
Correct Answer: Context switching between threads is faster and they share resources
Explanation:
Threads within the same process share code and data sections, making creation and context switching significantly lighter/faster than full processes.
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45Which variable in a Semaphore implementation must be protected by a critical section?
A.The process ID
B.The integer value of the semaphore
C.The system clock
D.The name of the semaphore
Correct Answer: The integer value of the semaphore
Explanation:
The integer value determines the state of the resource. Modifications to it (increments/decrements) must be atomic to prevent race conditions.
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46What is the Resource Allocation Graph (RAG) used for?
A.Visualizing memory allocation
B.Scheduling CPUs
C.Managing file permissions
D.Detecting Deadlocks
Correct Answer: Detecting Deadlocks
Explanation:
A RAG is a directed graph where cycles can indicate the presence of a deadlock (if there is only one instance of each resource type).
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47In Demand Paging, when is a page brought into memory?
A.When the process starts
B.Every 5 milliseconds
C.Before the CPU schedules the process
D.Only when it is explicitly requested/accessed during execution
Correct Answer: Only when it is explicitly requested/accessed during execution
Explanation:
Demand paging loads pages only when a page fault occurs (i.e., the page is needed), reducing I/O and memory usage.
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48If the Time Quantum in Round Robin scheduling is extremely large, the algorithm behaves like:
A.Multilevel Queue
B.Shortest Job First (SJF)
C.First-Come, First-Served (FCFS)
D.Priority Scheduling
Correct Answer: First-Come, First-Served (FCFS)
Explanation:
If the quantum is larger than the longest burst time, the process finishes without interruption, making it identical to FCFS.
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49Which memory placement strategy allocates the smallest hole that is big enough?
A.First-Fit
B.Best-Fit
C.Worst-Fit
D.Next-Fit
Correct Answer: Best-Fit
Explanation:
Best-Fit searches the entire list for the smallest hole that fits the process. This produces the smallest leftover hole.
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50What distinguishes User-Level Threads from Kernel-Level Threads?
A.Kernel threads are faster to create
B.User threads are managed by a library without kernel support
C.User threads are managed by the kernel
D.User threads can run on different processors simultaneously
Correct Answer: User threads are managed by a library without kernel support
Explanation:
User-level threads are managed in user space. The kernel is unaware of them, so if one blocks, the entire process blocks (in Many-to-One models).