1. What is an "Operating System" (OS)?

An Operating System is a software program that acts as an intermediary between the computer user and the computer hardware. Its primary goal is to provide an environment in which a user can execute programs in a convenient and efficient manner.

2. What are the key functions of an OS?

Process Management
Memory Management
File Management
I/O Device Management
Security and Protection
Job Accounting

3. What is a "Kernel"?

The core component of an Operating System that manages system resources and serves as a bridge between the software and the hardware. It is the first part of the OS loaded into memory during booting.

4. What are the types of Kernels?

Monolithic Kernel: All OS services run in the kernel space (e.g., Linux).
Microkernel: Minimal services in kernel space; others run in user space (e.g., QNX, L4).
Hybrid Kernel: A combination of both (e.g., Windows NT, macOS).

5. What is "Multitasking"?

The ability of an OS to execute more than one task (process) simultaneously on a single CPU by switching between them very quickly (Time Sharing).

6. What is "Multiprocessing"?

The use of two or more Central Processing Units (CPUs) within a single computer system to execute multiple processes at the same time.

7. What is "Multithreading"?

A technique where a single process is divided into multiple threads of execution that share the same memory space but run independently.

8. What is a "Process"?

A program in execution. It is an active entity that requires resources like CPU time, memory, files, and I/O devices to accomplish its task.

9. What is a "Thread"?

The smallest unit of execution within a process. Multiple threads within the same process share the same code segment, data segment, and OS resources.

10. What is the difference between a "Process" and a "Thread"?

Process: Independent; has its own memory; context switching is slower.
Thread: Subset of a process; shares memory; context switching is faster.

11. What is "Context Switching"?

The process of saving the state (context) of a running process or thread so that it can be restored and resume execution later. This allows the CPU to switch between multiple processes.

12. What is "Process Control Block" (PCB)?

A data structure used by the OS to store all the information about a process (e.g., process ID, state, program counter, CPU registers, memory limits).

13. What are the different "Process States"?

New: The process is being created.
Ready: The process is waiting to be assigned to a CPU.
Running: The process is currently executing instructions.
Waiting/Blocked: The process is waiting for some event (like I/O) to occur.
Terminated/Exit: The process has finished execution.

14. What is "CPU Scheduling"?

The process by which the OS decides which process in the ready queue should be assigned to the CPU for execution.

15. What are the common CPU Scheduling Algorithms?

First-Come, First-Served (FCFS)
Shortest Job First (SJF)
Priority Scheduling
Round Robin (RR)
Multilevel Queue Scheduling

16. What is "Starvation" in Scheduling?

A situation where a low-priority process is never executed because high-priority processes keep arriving (solved by Ageing).

17. What is "Ageing"?

A technique used to gradually increase the priority of processes that have been waiting in the system for a long time.

18. What is "Deadlock"?

A situation where a set of processes are blocked because each process is holding a resource and waiting for another resource held by another process in the same set.

19. What are the four "Necessary Conditions for Deadlock"?

Mutual Exclusion: Only one process can use a resource at a time.
Hold and Wait: A process holds a resource while waiting for another.
No Preemption: Resources cannot be forcibly taken from a process.
Circular Wait: A set of processes are waiting for each other in a circular chain.

20. How can we "Handle Deadlocks"?

Prevention: Ensuring at least one of the four conditions never holds.
Avoidance: Using algorithms like Banker's Algorithm to ensure the system remains in a safe state.
Detection and Recovery: Letting the deadlock occur and then resolving it.
Ignorance: Assuming deadlocks never happen (Ostrich Algorithm).

21. What is "Memory Management"?

The task of managing the computer's primary memory (RAM), keeping track of which parts are currently in use and by whom.

22. What is "Virtual Memory"?

A memory management technique that creates the illusion of a very large main memory by using a portion of the hard disk as an extension of RAM.

23. What is "Paging"?

A memory management scheme that eliminates the need for contiguous allocation of physical memory. It divides the process into "pages" and the physical memory into "frames."

24. What is a "Page Table"?

A data structure used by the OS to store the mapping between a process's logical addresses (pages) and clinical physical addresses (frames).

25. What is a "Page Fault"?

An interrupt that occurs when a program tries to access a page that is not currently mapped into physical memory (RAM).

26. What is "Segmentation"?

A memory management scheme that divides the logical address space of a process into segments based on its actual structure (e.g., code, data, stack).

27. What is "Thrashing"?

A situation where the system spends more time moving pages in and out of memory (swapping) than actually executing instructions, leading to a drastic drop in performance.

28. What is "Demand Paging"?

A type of paging where a page is only brought into physical memory when it is actually needed (requested).

29. What is "Fragmentation" in memory?

Internal: Unused space within an allocated memory block.
External: Total free memory is sufficient but not contiguous.

30. What is "Swapping"?

The process of moving a process from main memory to disk (backing store) and later bringing it back into memory for execution.

31. What is a "File System"?

A structure that the OS uses to organize and manage files on a storage device (e.g., NTFS, FAT32, ext4).

32. What is an "Inode"?

In Unix-like file systems, a data structure that stores all information about a file except its name and actual data (e.g., permissions, owner, size, pointers to data blocks).

33. What is "I/O Buffering"?

The process of temporarily storing data in memory while it is being transferred between two devices or between a device and an application.

34. What is "Spooling" (Simultaneous Peripheral Operations On-Line)?

A technique where data is sent to an intermediate or stationary storage area (like a disk) before being sent to its final destination (like a printer).

35. What is "Dynamic Linking" vs "Static Linking"?

Static: The library code is included in the executable file at build time.
Dynamic: The library code is loaded into memory only when the program is executed.

36. What is "Real-Time Operating System" (RTOS)?

An OS designed to handle requests and provide results within a strict time constraint (e.g., used in medical systems, aviation, industrial control).

37. What is "Shell"?

A user interface that allows you to interact with the OS by typing commands. It acts as a command interpreter.

38. What is a "System Call"?

A programmatic way in which a computer program requests a service from the kernel of the OS it is executed on.

39. What is "Belady's Anomaly"?

A phenomenon where increasing the number of page frames results in an increase in the number of page faults for certain access patterns (occurs in FIFO page replacement).

40. What is "Cache Memory"?

A small, high-speed memory located near the CPU that stores frequently used data and instructions to speed up access.

41. What is "Booting"?

The process of starting or restarting a computer, which involves loading the OS from the disk into the RAM.

42. What is "BIOS" (Basic Input/Output System)?

The first software that runs when you turn on your computer; it performs a Power-On Self-Test (POST) and initializes hardware.

43. What is "Inter-Process Communication" (IPC)?

A set of methods that allow different processes to communicate and synchronize their actions (e.g., Pipes, Message Queues, Shared Memory, Semaphores).

44. What is a "Semaphore"?

A synchronization tool (a variable or abstract data type) used to control access to a common resource by multiple processes in a concurrent system.

45. What is the "Critical Section" problem?

A segment of code where shared resources are accessed. To avoid data inconsistency, only one process should be allowed to execute in its critical section at a time.

46. What is "Mutual Exclusion" (Mutex)?

A property that ensures that no two processes can be in their critical sections at the same time.

47. What is "Banker's Algorithm"?

A resource allocation and deadlock avoidance algorithm that determines if a system is in a "safe state" before granting a resource request.

48. What is "RAID" (Redundant Array of Independent Disks)?

A technology that combines multiple physical disk drives into a single logical unit for data redundancy and performance improvement.

49. What is "Device Driver"?

A piece of software that allows the OS and other applications to communicate with a specific piece of hardware (e.g., printer, graphics card).

50. What is the "GUI" vs "CLI"?

GUI (Graphical User Interface): Uses icons, buttons, and windows (user-friendly).
CLI (Command Line Interface): Uses text-based commands (powerful for advanced users).

Operating System Interview Questions

Table of Contents

What is an "Operating System" (OS)?

What are the key functions of an OS?

What is a "Kernel"?

What are the types of Kernels?

What is "Multitasking"?

What is "Multiprocessing"?

What is "Multithreading"?

What is a "Process"?

What is a "Thread"?

What is the difference between a "Process" and a "Thread"?

What is "Context Switching"?

What is "Process Control Block" (PCB)?

What are the different "Process States"?

What is "CPU Scheduling"?

What are the common CPU Scheduling Algorithms?

What is "Starvation" in Scheduling?

What is "Ageing"?

What is "Deadlock"?

What are the four "Necessary Conditions for Deadlock"?

How can we "Handle Deadlocks"?

What is "Memory Management"?

What is "Virtual Memory"?

What is "Paging"?

What is a "Page Table"?

What is a "Page Fault"?

What is "Segmentation"?

What is "Thrashing"?

What is "Demand Paging"?

What is "Fragmentation" in memory?

What is "Swapping"?

What is a "File System"?

What is an "Inode"?

What is "I/O Buffering"?

What is "Spooling" (Simultaneous Peripheral Operations On-Line)?

What is "Dynamic Linking" vs "Static Linking"?

What is "Real-Time Operating System" (RTOS)?

What is "Shell"?

What is a "System Call"?

What is "Belady's Anomaly"?

What is "Cache Memory"?

What is "Booting"?

What is "BIOS" (Basic Input/Output System)?

What is "Inter-Process Communication" (IPC)?

What is a "Semaphore"?

What is the "Critical Section" problem?

What is "Mutual Exclusion" (Mutex)?

What is "Banker's Algorithm"?

What is "RAID" (Redundant Array of Independent Disks)?

What is "Device Driver"?

What is the "GUI" vs "CLI"?