1. Which scheduling algorithm gives the minimum average waiting time?
A) FCFS
B) Round Robin
C) Shortest Job First (SJF)
D) Priority Scheduling
✅ Answer: C) Shortest Job First (SJF)
💡 Explanation: SJF (Shortest Job First) is proven to give minimum average waiting time among all scheduling algorithms.
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2. A deadlock requires all four Coffman conditions. Which is NOT one of them?
A) Mutual Exclusion
B) Hold and Wait
C) Preemption
D) Circular Wait
✅ Answer: C) Preemption
💡 Explanation: The four Coffman conditions are: Mutual Exclusion, Hold & Wait, No Preemption, and Circular Wait.
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3. In virtual memory, the page replacement algorithm with the lowest page fault rate is theoretically:
A) LRU
B) FIFO
C) Optimal (OPT)
D) Clock
✅ Answer: C) Optimal (OPT)
💡 Explanation: The Optimal (OPT) page replacement algorithm has the lowest page fault rate but requires future knowledge.
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4. Thrashing in an OS occurs when:
A) Too many processes run simultaneously causing excessive paging
B) CPU utilization is too high
C) Hard disk is full
D) RAM is upgraded
✅ Answer: A) Too many processes run simultaneously causing excessive paging
💡 Explanation: Thrashing is when the OS spends more time swapping pages than executing processes.
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5. Which Linux command displays all running processes?
A) ls -a
B) ps aux
C) top -l
D) proc list
✅ Answer: B) ps aux
💡 Explanation: The ‘ps aux’ command shows all running processes with user, CPU, memory and other details.
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6. A process in ‘zombie state’ means:
A) Process is waiting for I/O
B) Process has finished but its entry is still in process table
C) Process is consuming maximum CPU
D) Process is blocked
✅ Answer: B) Process has finished but its entry is still in process table
💡 Explanation: A zombie process has completed execution but its entry remains in the process table awaiting parent to read exit status.
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7. Segmentation in memory management is different from paging because:
A) Segmentation uses fixed-size blocks
B) Segmentation uses variable-length segments based on logical divisions
C) Segmentation is faster
D) Segmentation is only for virtual memory
✅ Answer: B) Segmentation uses variable-length segments based on logical divisions
💡 Explanation: Segmentation divides memory into variable-size logical units (code, data, stack), unlike fixed-size pages.
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8. What is a semaphore in OS?
A) A type of memory
B) A synchronization primitive for controlling access to shared resources
C) A scheduling algorithm
D) A file system type
✅ Answer: B) A synchronization primitive for controlling access to shared resources
💡 Explanation: A semaphore is an integer variable used for inter-process synchronization and mutual exclusion.
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9. Which OS concept allows multiple users to simultaneously use a computer?
A) Multitasking
B) Time-sharing
C) Real-time processing
D) Batch processing
✅ Answer: B) Time-sharing
💡 Explanation: Time-sharing systems allocate CPU time slices to multiple users, making it seem all are running simultaneously.
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10. The ‘fork()’ system call in Unix/Linux:
A) Terminates a process
B) Creates a child process as a copy of the parent
C) Loads a new program
D) Creates a new thread
✅ Answer: B) Creates a child process as a copy of the parent
💡 Explanation: fork() creates a duplicate of the calling process (child). Both parent and child continue execution.
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11. NTFS is a file system used in:
A) Linux
B) macOS
C) Windows
D) Android
✅ Answer: C) Windows
💡 Explanation: NTFS (New Technology File System) is the primary file system for Windows NT and later versions.
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12. What is the role of the kernel in an OS?
A) Provides user interface
B) Manages hardware and system resources
C) Runs application software
D) Handles network connections only
✅ Answer: B) Manages hardware and system resources
💡 Explanation: The kernel is the core of the OS, managing CPU, memory, I/O devices, and system calls.
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13. Spooling stands for:
A) Simultaneous Peripheral Operations On-Line
B) System Process Online Operations Linking
C) Synchronized Peripheral Output Line
D) Standard Process Operation Linking
✅ Answer: A) Simultaneous Peripheral Operations On-Line
💡 Explanation: Spooling allows multiple programs to send data to a slow device (like printer) by buffering jobs.
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14. In Round Robin scheduling, a ‘time quantum’ refers to:
A) Total execution time of a process
B) Maximum time a process can run before being preempted
C) Time taken to switch context
D) Priority value of a process
✅ Answer: B) Maximum time a process can run before being preempted
💡 Explanation: The time quantum (time slice) is the fixed time period each process gets before the CPU switches to next.
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15. What is ‘context switching’ in operating systems?
A) Switching between user and kernel mode
B) Saving and restoring state of a process when switching CPU to another process
C) Changing file system context
D) Switching between hardware modes
✅ Answer: B) Saving and restoring state of a process when switching CPU to another process
💡 Explanation: Context switching saves a process’s state (registers, PC, etc.) so the CPU can run another process and resume later.
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16. Which memory allocation strategy suffers the most from external fragmentation?
A) Best Fit
B) Worst Fit
C) First Fit
D) All equally
✅ Answer: A) Best Fit
💡 Explanation: Best Fit leaves smallest unusable holes everywhere, causing the most external fragmentation over time.
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17. The inode in Unix/Linux stores:
A) File name
B) File metadata (permissions, size, timestamps, data block pointers)
C) Directory structure
D) User credentials
✅ Answer: B) File metadata (permissions, size, timestamps, data block pointers)
💡 Explanation: An inode contains all file metadata except the filename; the filename-to-inode mapping is in the directory.
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18. A critical section in OS refers to:
A) Most important section of the kernel
B) Code segment that accesses shared resources and must not be executed concurrently
C) Section of memory reserved for OS
D) High-priority processes
✅ Answer: B) Code segment that accesses shared resources and must not be executed concurrently
💡 Explanation: A critical section is a code region accessing shared data that requires mutual exclusion for correctness.
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19. Which scheduling is used in real-time operating systems?
A) FCFS
B) Rate Monotonic Scheduling
C) Round Robin
D) SJF
✅ Answer: B) Rate Monotonic Scheduling
💡 Explanation: Rate Monotonic Scheduling (RMS) is a fixed-priority preemptive algorithm commonly used in real-time OS.
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20. The term ‘kernel panic’ in Linux is equivalent to what in Windows?
A) System Idle
B) Blue Screen of Death (BSOD)
C) Application crash
D) Disk error
✅ Answer: B) Blue Screen of Death (BSOD)
💡 Explanation: Kernel panic (Linux) and BSOD (Windows) both indicate fatal OS errors that halt the system.
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