Must-Know Operating System Interview Questions

Friends If you are preparing for a operating system interview questions, it is very important to know about Operating System (OS). It is the most important software of the computer, which coordinates between the hardware and other programs. Without an operating system, the computer cannot function.

In this article, we will tell you about some easy and important operating system interview questions. These questions will help you strengthen your understanding and perform well in the interview. So, let’s start learning!

Common Operating System Interview Questions

What is an Operating System?

Answer: An Operating System (OS) is system software that manages hardware and software resources and provides services for computer programs.

Explanation: It acts as an intermediary between the user and hardware, ensuring smooth execution of applications. Examples include Windows, Linux, and macOS.

What are the main functions of an Operating System?

Answer:

1. Process Management
2. Memory Management
3. File System Management
4. Device Management
5. Security and Access Control
6. User Interface

Explanation: The OS ensures efficient resource allocation, user interaction, and system stability.

What is the difference between Process and Thread?

Answer:

• Process: An independent program in execution with its own memory space.
• Thread: A smaller unit within a process that shares memory and resources.

Explanation: Threads allow parallel execution within the same process, improving efficiency.

What is Virtual Memory?

Answer: Virtual Memory is a technique that allows the system to use a portion of the hard drive as additional RAM when physical memory is full.

Explanation: It enables larger programs to run and prevents memory shortages by swapping data between RAM and disk.

What is a Deadlock in OS?

Answer: A deadlock occurs when two or more processes are stuck, each waiting for a resource held by another process, preventing further execution.

Explanation: Deadlocks can be prevented by techniques like resource allocation ordering, avoiding circular wait, and using timeouts.

What are the different types of Scheduling Algorithms?

Answer:

1. First Come First Serve (FCFS)
2. Shortest Job Next (SJN or SJF)
3. Round Robin (RR)
4. Priority Scheduling
5. Multilevel Queue Scheduling

Explanation: Scheduling algorithms determine the order in which processes are executed in the CPU.

What is Paging in OS?

Answer: Paging is a memory management scheme that breaks the memory into fixed-size blocks called pages, which are mapped to frames in physical memory.

Explanation: It prevents external fragmentation and ensures efficient memory allocation.

What is the difference between Paging and Segmentation?

Answer:

• Paging: Divides memory into fixed-size blocks (pages).
• Segmentation: Divides memory based on logical units like functions, arrays, and procedures.

Explanation: Paging is fixed-sized, whereas segmentation is variable-sized and based on program structure.

What is Thrashing in an Operating System?

Answer: Thrashing occurs when excessive paging slows down the system performance because the CPU spends more time swapping pages in and out of memory than executing processes.

Explanation: It can be avoided by using proper page replacement policies and increasing RAM.

What are the Different Types of Kernels?

Answer:

1. Monolithic Kernel – Entire OS runs in kernel mode (e.g., Linux).
2. Microkernel – Minimal functions in kernel, rest in user mode (e.g., Minix).
3. Hybrid Kernel – Mix of monolithic and microkernel (e.g., Windows).
4. Exokernel – Provides direct hardware access to applications.

Explanation: The kernel is the core of an OS that manages system operations and hardware.

What is a Context Switch?

Answer: A context switch occurs when the CPU switches from one process or thread to another, saving and restoring its state.

Explanation: It enables multitasking but introduces overhead due to saving/restoring process states.

What is a File System?

Answer: A file system organizes and manages data storage on a disk, allowing users to store, retrieve, and modify files.

Explanation: Examples include FAT32, NTFS, and ext4. It provides structure and access control for files.

What is the difference between Multiprogramming, Multitasking, and Multiprocessing?

Answer:

• Multiprogramming: Multiple processes are loaded in memory but only one runs at a time.
• Multitasking: Multiple tasks share CPU time, switching rapidly.
• Multiprocessing: Uses multiple CPUs to execute multiple processes simultaneously.

Explanation: These techniques improve system performance and resource utilization.

What is a Semaphore?

Answer: A semaphore is a synchronization mechanism used to control access to shared resources in concurrent processes.

Explanation: It helps prevent race conditions and deadlocks. There are two types:

1. Binary Semaphore (0 or 1)
2. Counting Semaphore (non-negative integer)

What is Demand Paging?

Answer: Demand paging loads pages into memory only when they are needed, rather than preloading them.

Explanation: This reduces memory usage and improves performance by minimizing unnecessary page loads.

Operating System Interview Questions For beginners

What is Booting in an Operating System?

Answer: Booting is the process of starting a computer by loading the operating system into memory.

Explanation: When you turn on a computer, the BIOS/UEFI loads the OS from the storage device into RAM, making the system ready for use.

What is the Difference Between GUI and CLI?

Answer:

• GUI (Graphical User Interface): Uses icons, buttons, and menus for interaction (e.g., Windows, macOS).
• CLI (Command Line Interface): Requires text-based commands (e.g., Linux Terminal, Command Prompt).

Explanation: GUI is user-friendly, while CLI is more powerful for advanced users and automation.

What is a Shell in an OS?

Answer: A shell is an interface between the user and the operating system that allows command execution.

Explanation: Shells can be command-line based (Bash, PowerShell) or graphical. It interprets user commands and interacts with the kernel.

What is BIOS?

Answer: BIOS (Basic Input/Output System) is firmware that initializes hardware and loads the OS when a computer starts.

Explanation: BIOS runs before the OS and ensures essential components like the keyboard, storage, and display are working.

What are System Calls in an OS?

Answer: System calls are functions used by programs to request services from the operating system, such as file handling, process control, and memory management.

Explanation: They act as an interface between user applications and the OS kernel. Examples include read(), write(), and fork().

What is the Difference Between Kernel Mode and User Mode?

Answer:

• Kernel Mode: The OS runs with full access to hardware and system resources.
• User Mode: Applications run with limited access, ensuring security and stability.

Explanation: The CPU switches between these modes to protect critical system processes from user applications.

What is a Warm Boot and a Cold Boot?

Answer:

• Cold Boot: Turning on the computer after it has been completely shut down.
• Warm Boot: Restarting the system without turning off the power, usually using the restart option.

Explanation: Cold boot initializes all hardware, while warm boot reloads the OS without complete power cycling.

What is Spooling in an Operating System?

Answer: Spooling (Simultaneous Peripheral Operations On-Line) is a technique where data is temporarily stored in a buffer before being sent to a device like a printer.

Explanation: It allows multiple processes to queue tasks without waiting, improving efficiency.

What is Fragmentation in OS Memory Management?

Answer: Fragmentation occurs when memory is inefficiently used, leading to small unusable gaps.

Explanation: There are two types:

• Internal Fragmentation: Unused memory inside allocated blocks.
• External Fragmentation: Free memory scattered across non-contiguous blocks.

What is an Interrupt in an OS?

Answer: An interrupt is a signal that temporarily halts the CPU’s current execution to handle a high-priority event.

Explanation: Interrupts can be hardware-based (keyboard input, mouse clicks) or software-based (system calls, errors).

What is a Swap Space?

Answer: Swap space is a portion of the hard disk used as virtual memory when RAM is full.

Explanation: It helps the system run larger applications by temporarily moving inactive processes from RAM to disk.

What is the Difference Between Multithreading and Multitasking?

Answer:

• Multithreading: A single process runs multiple threads simultaneously.
• Multitasking: The OS allows multiple processes to run concurrently.

Explanation: Multithreading improves efficiency within a single program, while multitasking allows multiple programs to run at once.

What is a Race Condition?

Answer: A race condition occurs when multiple threads or processes try to access and modify shared data simultaneously, leading to unpredictable results.

Explanation: Synchronization techniques like mutexes and semaphores prevent race conditions.

What is the Role of a Device Driver?

Answer: A device driver is software that allows the operating system to communicate with hardware devices like printers, keyboards, and graphics cards.

Explanation: Without drivers, the OS cannot control hardware components effectively.

What is the Difference Between a Hard Link and a Soft Link?

Answer:

• Hard Link: A direct reference to the original file’s data on disk. Deleting the original file does not affect the hard link.
• Soft Link (Symbolic Link): A pointer to the original file’s location. If the original file is deleted, the soft link becomes invalid.

Explanation: Hard links are more robust, while soft links are flexible for linking across different file systems.

Operating System Interview Questions For Experts

What is the difference between system software and application software?

Answer:
System software includes programs that manage hardware and provide a platform for application software, such as operating systems and utility programs.
Application software consists of programs designed for end-users, like word processors, web browsers, and media players.

What is the booting process in an operating system?

Answer:
The booting process is the sequence of steps the system takes to start up. It involves:

1. Power-on and hardware initialization
2. Loading the BIOS/UEFI
3. Locating the bootloader
4. Loading the operating system into memory
5. Starting system processes

What is a shell in an operating system?

Answer:
A shell is an interface that allows users to interact with the OS, either through a command-line interface (CLI) like Bash or a graphical user interface (GUI).

What is a real-time operating system (RTOS)?

Answer:
An RTOS is an OS designed for real-time applications where tasks must be completed within strict time constraints. Examples include systems in medical devices, industrial robots, and automotive controls.

What is the role of an interrupt in an OS?

Answer:
An interrupt is a signal sent to the processor to indicate an event that needs immediate attention, such as input from a keyboard, hardware failure, or a scheduled task execution.

What is memory fragmentation?

Answer:
Memory fragmentation occurs when free memory is divided into small, non-contiguous blocks, making it difficult to allocate large contiguous memory spaces. It can be internal (wasted space within allocated memory) or external (gaps between allocated blocks).

What is the difference between user mode and kernel mode?

Answer:
User mode is where applications run with restricted access to system resources. Kernel mode has full access to hardware and system resources, allowing the OS to manage critical functions.

What is the purpose of a swap space?

Answer:
Swap space is a section of the hard disk used as virtual memory when the physical RAM is full. It temporarily stores inactive processes to free up RAM for active tasks.

What is a process control block (PCB)?

Answer:
A PCB is a data structure that contains information about a process, including its process ID, state, CPU registers, memory limits, and scheduling information.

What is CPU scheduling, and why is it important?

Answer:
CPU scheduling is the process of determining which process gets CPU time next. It ensures fair resource allocation, improves system responsiveness, and maximizes CPU efficiency.

What are soft and hard real-time systems?

Answer:
A soft real-time system allows occasional deadline misses but still functions effectively (e.g., video streaming). A hard real-time system requires strict adherence to deadlines, as failure could result in serious consequences (e.g., airbag systems in cars).

What is an orphan process?

Answer:
An orphan process is a child process whose parent has terminated, leaving it without a supervising parent process. In UNIX-like systems, these are adopted by the “init” process.

What is the purpose of the inode in a file system?

Answer:
An inode is a data structure in UNIX-based file systems that stores metadata about a file, such as its size, permissions, ownership, and location on disk.

What is a daemon process?

Answer:
A daemon is a background process that runs continuously and performs system-related tasks, such as handling network requests or logging system activity.

What is the difference between a hard link and a soft link in file systems?

Answer:
A hard link is a direct reference to the original file, sharing the same inode number. Deleting the original file does not remove the hard link.
A soft link (symbolic link) is a pointer to the original file. If the original file is deleted, the soft link becomes broken.