Top 50 Computer Science Interview Questions and Answers

By / October 15, 2025

Top Interview Questions

📝 Introduction

Are you preparing for your next Computer Science interview? Whether you’re a fresher starting your career or a professional refreshing your basics, understanding the most asked concepts can give you a strong edge. In this detailed guide on Top 50 Computer Science Interview Questions and Answers, we’ve carefully selected Top Interview Questions that recruiters commonly ask in real interviews. Each question comes with a clear definition, detailed explanation, and practical examples, making it beginner-friendly and easy to understand. These concepts cover programming fundamentals, data structures, algorithms, databases, operating systems, and more. This guide is designed to help students, job seekers, and fresh graduates prepare effectively. You can also explore other related Top Interview Questions to boost your preparation: Let’s dive into these Top Interview Questions and get you ready to ace your interview!

1. What is an Algorithm?

Answer: An algorithm is a step-by-step set of instructions designed to perform a specific task or solve a problem. Explanation: In computer science, algorithms are the foundation of programming and problem-solving. They define the logical sequence of actions that a computer program must follow to achieve a goal. Algorithms can be simple (finding the largest number in a list) or complex (sorting millions of records efficiently). Why Important:
  • Algorithms ensure efficiency and correctness in programs.
  • They help optimize performance in terms of speed and memory.
  • Algorithms form the backbone of technical interviews, testing problem-solving ability.
Example: A simple algorithm to find the largest number in an array:
  1. Start with the first number as the largest.
  2. Compare each number in the array.
  3. Update the largest if a bigger number is found.
  4. Return the largest at the end.

2. What is Data Structure?

Answer: A data structure is a way of organizing and storing data in a computer so it can be used efficiently. Explanation: Data structures include arrays, linked lists, stacks, queues, trees, graphs, and hash tables. Each data structure is suited for specific types of problems. Why Important:
  • Determines efficiency of algorithms.
  • Helps in data retrieval, storage, and manipulation.
  • Core topic in interviews because it reflects how a candidate handles real-world problems.
Example: A stack works on LIFO (Last In, First Out). If you undo typing in a text editor, the last action is undone first.

3. What is a Database?

Answer: A database is an organized collection of data that can be stored, retrieved, and managed electronically. Explanation: Databases are managed using Database Management Systems (DBMS) such as MySQL, Oracle, or MongoDB. They allow operations like inserting, updating, and querying data efficiently. Why Important:
  • Essential for almost all modern applications.
  • Supports secure, consistent, and efficient data handling.
  • Interviewers expect freshers to know database basics as most applications depend on them.
Example: An e-commerce website stores user details, product information, and transactions in databases like MySQL or MongoDB.

4. What is Object-Oriented Programming (OOP)?

Answer: Object-Oriented Programming is a programming paradigm based on the concept of objects, which can contain data (fields) and methods (functions). Explanation: OOP principles include Encapsulation, Abstraction, Inheritance, and Polymorphism (OOPS Pillars). Why Important:
  • Makes code reusable and modular.
  • Helps in building complex systems in a structured manner.
  • Reduces code duplication through inheritance and polymorphism.
Example: In Java, a Car class can have properties (color, model) and methods (drive, stop). Multiple car objects can be created using the same class.

5. What is Operating System (OS)?

Answer: An Operating System is system software that manages computer hardware and provides services for application programs. Explanation: OS acts as a bridge between the user and the hardware. Common types include Windows, Linux, macOS, and Android. Why Important:
  • Provides resource management (CPU, memory, storage).
  • Ensures system security and multitasking.
  • Understanding OS helps freshers troubleshoot and optimize programs.
Example: When you open multiple apps on your phone, the OS handles task scheduling so apps don’t crash.

6. What is Computer Network?

Answer: A computer network is a collection of computers and devices connected together to share resources and information. Explanation: Networks can be classified as LAN, MAN, or WAN based on their size and range. Protocols like TCP/IP, HTTP, and FTP govern communication. Why Important:
  • Enables sharing of files, applications, and internet access.
  • Backbone of communication in modern businesses.
  • Networking concepts are common in interviews.
Example: The Internet is the largest computer network, connecting billions of devices worldwide.

7. What is Software Development Life Cycle (SDLC)?

Answer: SDLC is a process used to design, develop, test, and deploy software systematically. Explanation: SDLC phases include: Requirement Gathering → Design → Implementation → Testing → Deployment → Maintenance. Why Important:
  • Ensures project success and quality.
  • Reduces cost and development risks.
  • Interviewers ask this to test understanding of development workflows.
Example: Agile SDLC involves iterative development where features are delivered in sprints.

8. What is Compiler and Interpreter?

Answer:
  • Compiler: Converts the entire code into machine language before execution.
  • Interpreter: Translates code line-by-line during execution.
Explanation: Compiled languages (C, C++) run faster but take time to compile. Interpreted languages (Python, JavaScript) are slower but easier to debug. Why Important:
  • Helps freshers understand programming language behavior.
  • Useful in choosing the right language for a project.
Example:
  • C uses a compiler.
  • Python uses an interpreter.

9. What is Cloud Computing?

Answer: Cloud computing delivers computing services like servers, storage, and databases over the internet (“the cloud”). Explanation: It offers models like SaaS, PaaS, and IaaS. Cloud providers include AWS, Azure, and Google Cloud. Why Important:
  • Reduces infrastructure cost.
  • Enables scalability and flexibility.
  • Highly relevant as most companies adopt cloud-based systems.
Example: Gmail is a cloud-based service that allows users to store emails and access them from anywhere.

10. What is Cybersecurity?

Answer: Cybersecurity is the practice of protecting systems, networks, and programs from digital attacks. Explanation: Cybersecurity includes encryption, authentication, firewalls, and monitoring systems. Attacks include phishing, malware, and DDoS. Why Important:
  • Protects sensitive data from hackers.
  • Ensures system integrity and availability.
  • Interviewers ask to test awareness of IT risks.
Example: Banks use two-factor authentication (2FA) to secure online transactions.

11. What is the difference between HTTP and HTTPS?

Answer:
  • HTTP (HyperText Transfer Protocol): A protocol for transferring data over the web.
  • HTTPS (HyperText Transfer Protocol Secure): A secure version of HTTP that uses encryption (SSL/TLS).
Explanation: HTTP allows data transfer between a web browser and server but lacks encryption, making it vulnerable to attacks like data interception. HTTPS, on the other hand, encrypts communication to secure sensitive information like login credentials or payment details. Why Important:
  • HTTPS builds trust for websites, especially in e-commerce and banking.
  • Search engines like Google prefer HTTPS websites in SEO ranking.
  • Protects users from attacks like man-in-the-middle (MITM).
Example:
  • http://example.com (not secure).
  • https://example.com (secure, with a padlock icon in the browser).

12. What is Artificial Intelligence (AI)?

Answer: Artificial Intelligence is the simulation of human intelligence in machines, enabling them to perform tasks such as decision-making, problem-solving, and learning. Explanation: AI can be narrow AI (specific tasks like chatbots, face recognition) or general AI (human-like intelligence, still under research). Techniques include machine learning, deep learning, and natural language processing. Why Important:
  • AI powers modern applications like recommendation systems, self-driving cars, and voice assistants.
  • Understanding AI basics helps freshers align with industry trends.
  • Companies prefer candidates aware of AI concepts, even if not experts.
Example:
  • Narrow AI: Alexa, Siri.
  • AI in business: Netflix recommending movies.

13. What is the difference between Primary Key and Foreign Key?

Answer:
  • Primary Key: A unique identifier for each record in a database table.
  • Foreign Key: A column that establishes a link between two tables.
Explanation: The primary key ensures uniqueness (no duplicates, no nulls). The foreign key enforces referential integrity by linking related records in another table. Why Important:
  • Ensures data integrity in relational databases.
  • Helps structure data logically across multiple tables.
  • Common interview question in SQL/database rounds.
Example:
  • Table: Students (StudentID PRIMARY KEY, Name)
  • Table: Marks (MarkID, StudentID FOREIGN KEY, Score)
Here, StudentID links both tables.

14. What is Normalization in Databases?

Answer: Normalization is the process of organizing data in a database to reduce redundancy and improve data integrity. Explanation: There are multiple normal forms (1NF, 2NF, 3NF, BCNF). Each form removes specific issues like duplicate data, partial dependency, or transitive dependency. Why Important:
  • Reduces storage cost by eliminating redundancy.
  • Improves data consistency and efficiency.
  • Widely asked in DBMS interviews.
Example: Instead of storing student and course details repeatedly, we separate into:
  • Students (StudentID, Name)
  • Courses (CourseID, CourseName)
  • Enrollment (StudentID, CourseID)
 

15. What is Big Data?

Answer: Big Data refers to large and complex datasets that cannot be managed by traditional database systems. Explanation: Big Data is characterized by the 5 Vs: Volume, Velocity, Variety, Veracity, and Value. Technologies like Hadoop, Spark, and NoSQL are used to handle it. Why Important:
  • Businesses rely on Big Data for insights (customer behavior, fraud detection).
  • Data Science and AI depend heavily on Big Data processing.
  • Freshers should know basics as most industries now generate large datasets.
Example:
  • Social media platforms like Facebook process terabytes of data daily.
  • Amazon uses Big Data for personalized product recommendations.

16. What is a Programming Language?

Answer: A programming language is a formal language used to write instructions for a computer to execute. Explanation: Programming languages can be:
  • Low-level (C, Assembly): Closer to machine code.
  • High-level (Python, Java): Human-readable and abstracted. They can also be compiled (C++) or interpreted (Python).
Why Important:
  • Programming skills are core for computer science careers.
  • Each language is suited for specific applications (Java for enterprise apps, Python for AI).
  • Interviewers test fundamentals of at least one language.
Example:
  • Python: print(“Hello World”)
  • C++: cout << “Hello World”;

17. What is Recursion in Programming?

Answer: Recursion is a programming technique where a function calls itself directly or indirectly. Explanation: A recursive function typically has:
  1. Base case: Stops recursion.
  2. Recursive case: Function calls itself with a smaller input.
Why Important:
  • Useful in problems like tree traversal, factorial, Fibonacci series.
  • Tests candidate’s problem-solving ability in interviews.
  • Requires understanding of stack memory and function calls.
Example: Factorial using recursion: def factorial(n):     if n == 1:         return 1     return n * factorial(n – 1)  

18. What is the difference between Static and Dynamic Memory Allocation?

Answer:
  • Static Memory Allocation: Memory is allocated at compile time.
  • Dynamic Memory Allocation: Memory is allocated at runtime.
Explanation: Static allocation uses a fixed size (arrays). Dynamic allocation uses pointers and functions like malloc() in C. Why Important:
  • Efficient memory management is crucial in programming.
  • Interviewers check understanding of runtime vs compile-time concepts.
Example:
  • Static: int arr[5]; (size fixed).
  • Dynamic: int *arr = malloc(5 * sizeof(int)); (size flexible).

19. What is the difference between Process and Thread?

Answer:
  • Process: An independent program in execution.
  • Thread: A lightweight unit of execution within a process.
Explanation: Processes have separate memory; threads share memory within the same process. Threads improve performance by parallel execution but may face issues like synchronization. Why Important:
  • Essential for understanding multitasking and parallelism.
  • Common question in OS and system design interviews.
Example:
  • A browser is a process.
  • Multiple tabs inside the browser are threads.

20. What is Deadlock in Operating Systems?

Answer: Deadlock is a situation where two or more processes are blocked forever, waiting for each other’s resources. Explanation: Deadlocks occur when four conditions hold simultaneously:
  1. Mutual exclusion
  2. Hold and wait
  3. No preemption
  4. Circular wait
Why Important:
  • Affects system reliability.
  • Interviewers test knowledge of OS resource management.
Example: Process A holds resource X and waits for Y, while Process B holds Y and waits for X → both are stuck in deadlock.

21. What is an Operating System (OS)?

Answer: An Operating System (OS) is system software that manages computer hardware and software resources and provides services for applications and users. Explanation: The OS acts as a bridge between users and hardware. It handles:
  • Process management (running programs).
  • Memory management (allocation and release).
  • File system management (storing/retrieving data).
  • Device management (printers, disks).
  • Security and user interface (authentication, GUI).
OS types include:
  • Batch OS (early systems, no interaction).
  • Time-sharing OS (multiple users simultaneously).
  • Distributed OS (clustered systems).
  • Real-time OS (critical applications like autopilot systems).
Why Important:
  • OS knowledge is fundamental to computer science.
  • Many interview questions revolve around process scheduling, memory management, and deadlocks.
  • Freshers are expected to know OS concepts for coding and system design roles.
Example:
  • Windows, Linux, macOS (general-purpose OS).
  • Android, iOS (mobile OS).

22. What is Virtual Memory?

Answer: Virtual Memory is a memory management technique where the OS uses part of the hard disk as an extension of RAM. Explanation: When physical RAM is full, the OS moves less-used data into a disk area called swap space. This creates the illusion of having more memory than physically available. Virtual memory relies on paging and segmentation. Why Important:
  • Helps run large programs on small RAM.
  • Prevents crashes when memory demand exceeds physical RAM.
  • Essential OS concept in interviews.
Example: If a system has 4 GB RAM and runs a program needing 6 GB, the extra 2 GB is handled using virtual memory (swap file on disk).

23. What is Cloud Computing?

Answer: Cloud Computing is the delivery of computing resources (storage, servers, databases, networking, software) over the internet on a pay-as-you-go model. Explanation: Cloud models:
  • IaaS (Infrastructure-as-a-Service): Provides hardware resources (e.g., AWS EC2).
  • PaaS (Platform-as-a-Service): Provides environment for developers (e.g., Google App Engine).
  • SaaS (Software-as-a-Service): Provides ready-to-use applications (e.g., Gmail, Zoom).
Cloud deployment models: Public, Private, Hybrid, Multi-Cloud. Why Important:
  • Cloud is a key industry trend; companies shift from physical servers to cloud.
  • Knowledge of cloud basics (AWS, Azure, GCP) increases fresher employability.
Example:
  • Netflix uses AWS cloud for streaming.
  • Google Drive allows storage without worrying about physical hard drives.

24. What is a Database Management System (DBMS)?

Answer: A DBMS is software that helps create, manage, and manipulate databases efficiently. Explanation: A DBMS allows:
  • Data storage in structured form.
  • Querying using SQL.
  • Enforcing security and data integrity.
  • Multi-user access with concurrency control.
Types:
  • Relational DBMS (RDBMS): Uses tables (MySQL, PostgreSQL).
  • NoSQL DBMS: Stores unstructured/large-scale data (MongoDB, Cassandra).
Why Important:
  • Almost all applications need databases.
  • DBMS ensures data consistency, availability, and security.
  • SQL is a must-have skill for freshers.
Example:
  • Banking: storing customer accounts.
  • E-commerce: storing products, users, and orders.

25. What is SQL?

Answer: SQL (Structured Query Language) is a standard programming language used to interact with relational databases. Explanation: SQL allows:
  • Data Definition (DDL): Create/alter tables.
  • Data Manipulation (DML): Insert, update, delete data.
  • Data Querying (DQL): Select and filter records.
  • Data Control (DCL): Manage permissions.
Why Important:
  • SQL is essential for working with relational databases.
  • Used in analytics, software engineering, and data science.
  • Interviewers expect freshers to know basic SQL queries.
Example: CREATE TABLE Students (ID INT, Name VARCHAR(50)); INSERT INTO Students VALUES (1, ‘Amit’); SELECT * FROM Students;

26. What is Object-Oriented Programming (OOP)?

Answer: OOP is a programming paradigm based on the concept of “objects” that combine data (attributes) and methods (functions). Explanation: OOP principles:
  • Encapsulation: Wrapping data & methods together.
  • Inheritance: Reusing code by deriving new classes.
  • Polymorphism: Ability of methods to behave differently.
  • Abstraction: Hiding implementation details.
Why Important:
  • OOP is widely used in real-world applications (Java, Python, C++).
  • Helps organize large projects into reusable modules.
  • Often tested in interviews with coding exercises.
Example: class Car:     def __init__(self, brand):         self.brand = brand     def drive(self):         print(f”{self.brand} is driving”)   Creating an object: c = Car(“Tesla”) c.drive()

27. What is a Linked List?

Answer: A Linked List is a linear data structure where elements (nodes) are connected using pointers. Explanation: Each node contains:
  • Data (value).
  • Pointer (address of next node).
Types:
  • Singly Linked List: Points to next node only.
  • Doubly Linked List: Points to both next and previous nodes.
  • Circular Linked List: Last node points back to first.
Why Important:
  • Useful for dynamic memory allocation.
  • Interviewers ask linked list coding questions to test logic.
  • Unlike arrays, size can grow/shrink dynamically.
Example:
  • Singly linked list of numbers: 10 → 20 → 30.
  • Doubly linked list for playlist navigation (next/previous songs).

28. What is an Array?

Answer: An array is a collection of elements stored at contiguous memory locations and accessed using indices. Explanation: Arrays provide:
  • Fixed-size storage.
  • Fast access (O(1)) using index.
  • Can store primitive types or objects.
Why Important:
  • Fundamental data structure taught in CS.
  • Used in searching, sorting, and dynamic programming problems.
  • Frequently tested in coding interviews.
Example: arr = [10, 20, 30, 40] print(arr[2])   # Output: 30  

29. What is a Stack?

Answer: A Stack is a linear data structure that follows the LIFO (Last In, First Out) principle. Explanation:
  • Operations: Push (insert), Pop (remove), Peek (top element).
  • Implemented using arrays or linked lists.
Why Important:
  • Used in function calls, undo operations, and expression evaluation.
  • Interviewers often ask to implement stack logic.
Example:
  • Browser back/forward navigation.
  • Reversing a string using stack.
Python example: stack = [] stack.append(10)   # Push stack.pop()        # Pop  

30. What is a Queue?

Answer: A Queue is a linear data structure that follows the FIFO (First In, First Out) principle. Explanation:
  • Operations: Enqueue (insert), Dequeue (remove).
  • Types:
    • Simple Queue (basic).
    • Circular Queue (efficient memory use).
    • Priority Queue (based on priority).
Why Important:
  • Used in task scheduling, CPU processes, printer spooling.
  • Key concept in OS and system design interviews.
Example:
  • Ticket booking system where first customer is served first.
  • Print queue in an office.
Python example: from collections import deque queue = deque([1,2,3]) queue.append(4)     # Enqueue queue.popleft()     # Dequeue  

31. What is a Hash Table?

Answer: A Hash Table is a data structure that stores key-value pairs and allows fast data retrieval using a hashing function. Explanation:
  • A hash function maps keys to an index in an array (called a hash table).
  • If two keys map to the same index (collision), techniques like chaining or open addressing are used.
  • Hash tables provide average O(1) time complexity for insertion, deletion, and search.
Why Important:
  • Fundamental for building efficient lookup systems.
  • Used in compilers, caching, and databases.
  • Interviewers often test hash table coding to check logical understanding.
Example:
  • Python dict is implemented using hash tables.
students = {“Amit”: 90, “Riya”: 85} print(students[“Amit”])  # 90  
  • Real-world use: telephone directory mapping names → phone numbers.

32. What is Recursion?

Answer: Recursion is a programming technique where a function calls itself directly or indirectly to solve a problem. Explanation:
  • Every recursive function has:
    • Base case (stopping condition).
    • Recursive case (function calls itself).
  • Commonly used in divide-and-conquer algorithms.
Why Important:
  • Recursion simplifies code for tree/graph traversal, factorial, Fibonacci, etc.
  • Interviewers test recursion to evaluate problem-solving skills.
Example: Factorial using recursion: def fact(n):     if n == 0: return 1     return n * fact(n-1) print(fact(5))  # 120  
  • Real-world use: file system navigation (folders within folders).

33. What is Dynamic Programming (DP)?

Answer: Dynamic Programming is an optimization technique used to solve problems by breaking them into smaller subproblems and storing their results to avoid recalculation. Explanation:
  • Relies on overlapping subproblems and optimal substructure.
  • Techniques:
    • Top-down (memoization): recursion + caching.
    • Bottom-up (tabulation): iterative approach.
Why Important:
  • Essential for solving complex algorithmic problems efficiently.
  • Common in competitive programming and technical interviews.
Example: Fibonacci with DP: def fib(n, memo={}):     if n in memo: return memo[n]     if n <= 1: return n     memo[n] = fib(n-1, memo) + fib(n-2, memo)     return memo[n]  
  • Real-world use: shortest path algorithms (Dijkstra, Bellman-Ford).

34. What is Computer Networking?

Answer: Computer Networking is the practice of connecting multiple devices to share resources and data. Explanation:
  • Types: LAN, WAN, MAN, PAN.
  • Topologies: Bus, Star, Ring, Mesh, Hybrid.
  • Uses protocols like TCP/IP, HTTP, FTP, SMTP.
Why Important:
  • Networking enables communication between computers, mobile devices, and servers.
  • Essential knowledge for jobs in IT, cloud, and security.
Example:
  • LAN in offices for file and printer sharing.
  • Internet is the largest WAN.
  • WhatsApp uses networking protocols to send/receive messages.

35. What is TCP/IP Model?

Answer: The TCP/IP (Transmission Control Protocol/Internet Protocol) model is a networking framework that defines communication across networks. Explanation: Layers of TCP/IP:
  1. Application Layer: (HTTP, FTP, SMTP).
  2. Transport Layer: (TCP – reliable, UDP – fast but unreliable).
  3. Internet Layer: (IP, ICMP).
  4. Network Access Layer: (Ethernet, Wi-Fi).
Why Important:
  • Internet runs on TCP/IP.
  • Interviewers expect basic networking knowledge from freshers.
Example:
  • When you open a website:
    • HTTP (Application) requests a page.
    • TCP (Transport) ensures data reaches correctly.
    • IP (Internet) routes packets.
    • Ethernet/Wi-Fi (Network) delivers it.

36. What is Big O Notation?

Answer: Big O Notation describes the time or space complexity of an algorithm in terms of input size. Explanation:
  • Common complexities:
    • O(1) → Constant.
    • O(log n) → Logarithmic.
    • O(n) → Linear.
    • O(n log n) → Efficient sorting.
    • O(n²) → Nested loops.
Why Important:
  • Helps evaluate algorithm efficiency.
  • Key interview topic for coding roles.
Example:
  • Searching in an unsorted array → O(n).
  • Binary Search → O(log n).
  • Sorting using Merge Sort → O(n log n).

37. What is Artificial Intelligence (AI)?

Answer: Artificial Intelligence is the simulation of human intelligence in machines that can learn, reason, and make decisions. Explanation:
  • Narrow AI: Specialized tasks (Siri, Google Assistant).
  • General AI: Human-like intelligence (still research).
  • Machine Learning (ML): Subset of AI using data-driven models.
  • Deep Learning (DL): Neural networks for advanced tasks.
Why Important:
  • AI drives modern applications (self-driving cars, chatbots).
  • Essential knowledge for fresher jobs in data science and software development.
Example:
  • Netflix recommending movies.
  • Tesla Autopilot using AI to drive safely.

38. What is Machine Learning (ML)?

Answer: Machine Learning is a subset of AI that enables systems to learn patterns from data without being explicitly programmed. Explanation:
  • Types of ML:
    • Supervised Learning (labeled data, e.g., spam detection).
    • Unsupervised Learning (unlabeled data, e.g., clustering).
    • Reinforcement Learning (reward-based learning, e.g., robotics).
Why Important:
  • ML powers many modern apps.
  • Freshers with ML skills have higher job opportunities.
Example:
  • Email spam filter (supervised).
  • Customer segmentation (unsupervised).
  • Game AI (reinforcement).

39. What is Cybersecurity?

Answer: Cybersecurity refers to protecting computer systems, networks, and data from unauthorized access, attacks, and damage. Explanation:
  • Techniques: Encryption, Firewalls, Antivirus, Intrusion Detection.
  • Common threats: Malware, Phishing, Ransomware, DDoS attacks.
Why Important:
  • With increasing cyberattacks, companies demand secure systems.
  • Freshers need cybersecurity basics for IT roles.
Example:
  • HTTPS encryption secures online transactions.
  • Antivirus prevents malware infections.
  • Firewalls block unauthorized access.

40. What is Software Development Life Cycle (SDLC)?

Answer: SDLC is a structured process used to design, develop, test, and deploy software efficiently. Explanation: Phases of SDLC:
  1. Requirement Analysis.
  2. Design.
  3. Implementation (Coding).
  4. Testing.
  5. Deployment.
  6. Maintenance.
Models of SDLC: Waterfall, Agile, Spiral, V-Model. Why Important:
  • Ensures quality software delivery.
  • Interviewers often test SDLC knowledge for fresher software roles.
Example:
  • E-commerce website development follows SDLC:
    • Requirements → UI design → Backend coding → Testing → Deployment → Updates.

41. What is Cloud Computing?

Answer: Cloud computing is the delivery of computing resources—such as servers, storage, databases, networking, software, and analytics—over the internet (“the cloud”). Explanation:
  • Instead of owning physical hardware/software, users rent resources on demand.
  • Service Models:
    • IaaS (Infrastructure as a Service) – AWS EC2.
    • PaaS (Platform as a Service) – Google App Engine.
    • SaaS (Software as a Service) – Gmail, Zoom.
  • Deployment Models: Public, Private, Hybrid, and Multi-cloud.
Why Important:
  • Cloud reduces cost, increases scalability, and offers global accessibility.
  • Most modern companies run on cloud (AWS, Azure, GCP).
Example:
  • Netflix uses AWS to stream content worldwide.
  • Google Drive provides cloud storage.

42. What is Virtualization?

Answer: Virtualization is the creation of a virtual version of hardware, operating systems, storage, or networks using software. Explanation:
  • Hypervisor (VMware, VirtualBox) manages multiple virtual machines (VMs) on a single host.
  • Types:
    • Hardware virtualization.
    • OS-level virtualization (containers).
    • Storage and network virtualization.
Why Important:
  • Increases hardware utilization.
  • Reduces costs and enables cloud computing.
Example:
  • Running Windows and Linux on the same computer using VMware.
  • Docker containers virtualize applications for portability.

43. What is Operating System (OS)?

Answer: An Operating System is system software that manages computer hardware, software resources, and provides services to applications. Explanation:
  • Functions:
    • Process Management.
    • Memory Management.
    • File System Management.
    • Device Management.
    • Security and User Interface.
Why Important:
  • Without an OS, a computer cannot function.
  • Freshers must know OS concepts for interviews.
Example:
  • Windows, Linux, macOS, Android.
  • File Explorer (Windows) or ls (Linux) are OS-level services.

44. What is Deadlock in Operating Systems?

Answer: A deadlock is a situation in OS when two or more processes are waiting indefinitely for resources held by each other. Explanation: Deadlock conditions (Coffman’s conditions):
  1. Mutual Exclusion.
  2. Hold and Wait.
  3. No Preemption.
  4. Circular Wait.
Why Important:
  • Deadlocks can freeze systems.
  • OS designers must handle or avoid them.
Example:
  • Two processes:
    • P1 holds Printer, needs Scanner.
    • P2 holds Scanner, needs Printer.
    • Both wait forever → deadlock.
Solutions: Deadlock prevention, avoidance (Banker’s Algorithm), and detection.

45. What is Paging in OS?

Answer: Paging is a memory management scheme where processes are divided into fixed-size pages and loaded into memory frames. Explanation:
  • Eliminates external fragmentation.
  • Logical address space is divided into pages, physical memory into frames.
  • Page Table maps logical to physical addresses.
Why Important:
  • Efficient memory utilization.
  • Concept tested in OS interviews.
Example:
  • If a program is 8KB and page size is 2KB → 4 pages required.
  • Each page is loaded into available frames in RAM.
 

46. What is Multithreading?

Answer: Multithreading is the ability of a CPU or program to run multiple threads concurrently. Explanation:
  • A thread is the smallest unit of execution.
  • Multithreading allows tasks like I/O, computation, and UI updates to run in parallel.
  • Supported in Java, Python, and C++.
Why Important:
  • Improves efficiency and responsiveness.
  • Commonly used in modern applications.
Example:
  • Web browsers: one thread for UI, another for downloads.
  • Python example:
import threading   def print_numbers():     for i in range(5):         print(i)   t = threading.Thread(target=print_numbers) t.start()

47. What is Normalization in DBMS?

Answer: Normalization is the process of organizing a database to reduce redundancy and improve data integrity. Explanation:
  • Divides large tables into smaller related ones.
  • Forms:
    • 1NF: Atomic values.
    • 2NF: Remove partial dependency.
    • 3NF: Remove transitive dependency.
    • BCNF: Stronger version of 3NF.
Why Important:
  • Prevents anomalies in Insert, Update, Delete operations.
  • Ensures efficient database design.
Example:
  • Bad design:
    • Student(ID, Name, Course, Instructor).
  • Normalized:
    • Student(ID, Name).
    • Course(CourseID, Instructor).
    • Enrollment(ID, CourseID).

48. What is Denormalization in DBMS?

Answer: Denormalization is the process of adding redundancy into a database to improve performance. Explanation:
  • Opposite of normalization.
  • Reduces complex joins by combining tables.
  • Often used in data warehouses.
Why Important:
  • Faster queries in real-time applications.
  • Used in big data systems.
Example:
  • Instead of joining Order and Customer tables, store CustomerName directly in Orders table for faster reads.

49. What is Primary Key, Foreign Key, and Unique Key?

Answer:
  • Primary Key: Uniquely identifies a record in a table.
  • Foreign Key: Establishes a relationship between two tables.
  • Unique Key: Ensures all values in a column are unique.
Explanation:
  • Primary Key: only one per table, cannot be NULL.
  • Foreign Key: references a primary key in another table.
  • Unique Key: multiple allowed, one NULL permitted.
Why Important:
  • Maintains relational integrity in DBMS.
Example: CREATE TABLE Student (   StudentID INT PRIMARY KEY,   Name VARCHAR(50) );   CREATE TABLE Course (   CourseID INT PRIMARY KEY,   StudentID INT,   FOREIGN KEY (StudentID) REFERENCES Student(StudentID) );

50. What is Software Testing and its Types?

Answer: Software Testing is the process of evaluating software to ensure it meets requirements and is free of defects. Explanation:
  • Types:
    • Manual Testing: Human testers execute cases.
    • Automation Testing: Tools like Selenium, JUnit.
  • Levels: Unit, Integration, System, Acceptance.
  • Methods:
    • Black-box Testing – tests functionality.
    • White-box Testing – tests internal logic.
Why Important:
  • Ensures software quality, reliability, and security.
  • Critical step in SDLC.
Example:
  • Unit Test in Python:
def add(a, b): return a+b assert add(2,3) == 5
  • Real-world: Banking app tested for secure transactions.

✅ Conclusion

Mastering the Top Interview Questions in Computer Science can make a big difference in your job search. This list of Top 50 Computer Science Interview Questions and Answers is designed to build your core foundation and help you explain concepts confidently during technical interviews. Remember, interviewers value concept clarity, problem-solving ability, and practical application more than memorized answers. So, practice consistently, strengthen your fundamentals, and stay updated with industry trends. To continue your preparation, check out more Top Interview Questions guides here: With the right strategy and these Top Interview Questions, you’ll be one step closer to landing your dream job.  

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