Operating System Interview Questions & Answers (2025)

1. What is an Operating System?

An Operating System manages hardware resources and provides services to programs.

2. What are the main functions of an OS?

Process management, memory management, file system, and device management.

3. What are the types of Operating Systems?

Batch, Time-sharing, Distributed, Network, and Real-time OS.

4. What is a process?

A process is a program in execution.

5. What is a thread?

A thread is the smallest unit of execution within a process.

6. Difference between process and thread?

Processes are independent, threads share memory.

7. What is multitasking?

Executing multiple tasks simultaneously.

8. What is multiprocessing?

Using multiple CPUs to execute processes.

9. What is scheduling?

Deciding which process runs next.

10. What is CPU scheduling?

Managing execution of processes on CPU.

11. What are scheduling algorithms?

FCFS, SJF, Priority, Round Robin.

12. What is FCFS?

First Come First Serve scheduling.

13. What is SJF?

Shortest Job First scheduling.

14. What is Round Robin?

Each process gets fixed time slice.

15. What is Priority scheduling?

Processes are scheduled based on priority.

16. What is starvation?

Process waits indefinitely for CPU resources.

17. What is aging?

Technique to prevent starvation by increasing priority.

18. What is deadlock?

Processes waiting indefinitely for resources held by each other.

19. What are deadlock conditions?

Mutual exclusion, hold and wait, no preemption, circular wait.

20. What is deadlock prevention?

Ensuring at least one deadlock condition never occurs.

21. What is deadlock avoidance?

Avoiding deadlock by safe resource allocation.

22. What is Banker’s Algorithm?

Algorithm used for deadlock avoidance.

23. What is deadlock detection?

Detecting deadlock after it occurs.

24. What is recovery from deadlock?

Terminating processes or preempting resources.

25. What is memory management?

Managing main memory efficiently.

26. What is virtual memory?

Using disk space as an extension of RAM.

27. What is paging?

Memory management scheme dividing memory into pages.

28. What is segmentation?

Dividing memory into logical segments.

29. Difference between paging and segmentation?

Paging is fixed size, segmentation is variable size.

30. What is page fault?

Occurs when requested page is not in memory.

31. What is thrashing?

System spends more time paging than executing.

32. What is file system?

Organizes and stores files on storage devices.

33. What are file access methods?

Sequential, Direct, and Indexed access.

34. What is directory structure?

Organizes files into directories.

35. What is I/O management?

Managing input and output devices.

36. What is buffering?

Temporary storage of data during transfer.

37. What is spooling?

Overlapping I/O and CPU operations.

38. What is device driver?

Software that controls hardware devices.

39. What is interrupt?

Signal to CPU to stop current execution.

40. What is context switching?

Switching CPU from one process to another.

41. What is kernel?

Core part of OS managing system resources.

42. What are kernel types?

Monolithic, Microkernel, Hybrid.

43. What is system call?

Interface between user programs and OS.

44. What is user mode?

Restricted mode where user applications run.

45. What is kernel mode?

Privileged mode where OS runs.

46. What is booting?

Process of starting the computer.

47. What is BIOS?

Basic Input Output System initializes hardware.

48. What is UEFI?

Modern replacement for BIOS.

49. What is real-time OS?

OS that responds within strict time constraints.

50. What is hard real-time system?

Missing deadline causes system failure.

51. What is soft real-time system?

Deadlines are important but not fatal.

52. What is distributed OS?

OS managing multiple computers as one system.

53. What is network OS?

OS designed to manage network resources.

54. What is protection?

Controlling access to system resources.

55. What is security?

Preventing unauthorized access to system.

56. What is access control?

Defines who can access resources.

57. What is authentication?

Verifying user identity.

58. What is authorization?

Granting permissions to users.

59. What is shell?

Interface between user and operating system.

60. What is CLI?

Command Line Interface for interacting with OS.