Core CS Subjects
The four subjects every campus technical interview asks about — revise with cheat sheets, tables, top questions and quick quizzes.
Operating Systems
6 topics
Processes, threads, scheduling, deadlocks, memory and synchronization.
Start RevisionDatabase Management Systems
6 topics
ACID, normalization, keys, indexing, transactions and SQL vs NoSQL.
Start RevisionComputer Networks
6 topics
OSI/TCP-IP, TCP vs UDP, IP & subnetting, DNS, HTTP/HTTPS and routing.
Start RevisionObject-Oriented Programming
6 topics
Four pillars, classes & objects, SOLID, design patterns and low-level design.
Start RevisionProcesses vs Threads
A process is a program in execution with its own address space. A thread is the smallest unit of CPU scheduling and lives inside a process, sharing its memory with sibling threads.
CPU Scheduling
The scheduler picks which ready process gets the CPU. Algorithms trade off waiting time, response time, throughput and fairness.
Deadlocks
A deadlock is a set of processes each waiting for a resource held by another in the set, so none can proceed.
Memory Management & Paging
The OS maps logical addresses to physical memory. Paging splits memory into fixed-size frames to remove external fragmentation.
Virtual Memory & Page Replacement
Virtual memory lets processes use more memory than physically exists by keeping only needed pages in RAM (demand paging).
Synchronization: Mutex & Semaphores
When threads share data, a critical section must be protected to avoid race conditions. Mutexes and semaphores are the main tools.
ACID & Transactions
A transaction is a logical unit of work. ACID properties guarantee correctness even with crashes and concurrency.
Normalization (1NF → BCNF)
Normalization removes redundancy and update anomalies by decomposing tables based on functional dependencies.
Keys & ER Model
Keys uniquely identify rows and link tables. The ER model describes entities, attributes and relationships before building tables.
Indexing & B+ Trees
An index is an auxiliary structure that speeds up lookups at the cost of extra storage and slower writes.
Concurrency & Isolation Levels
Isolation levels trade correctness for concurrency by allowing certain read anomalies.
SQL vs NoSQL & CAP
Relational databases enforce schema and ACID; NoSQL databases favour flexible schema and horizontal scale.
OSI & TCP/IP Models
Layered models split networking into responsibilities so each layer serves the one above it.
TCP vs UDP & 3-Way Handshake
TCP provides reliable, ordered, connection-oriented delivery; UDP is lightweight, connectionless and best-effort.
IP Addressing & Subnetting
IP addresses identify hosts; subnetting splits a network into smaller networks using a subnet mask.
DNS, HTTP & HTTPS
DNS turns names into IPs; HTTP is the request/response protocol of the web; HTTPS secures it with TLS.
Routing & Switching
Routers choose paths between networks using routing tables built statically or by routing protocols.
Network Security & Sockets
Common attacks and defences, plus how applications talk over the network using sockets and WebSockets.
The Four Pillars
OOP organizes code around objects. Encapsulation, Abstraction, Inheritance and Polymorphism are its pillars.
Classes, Objects & Constructors
A class is a blueprint; an object is an instance in memory. Constructors initialize objects; destructors clean them up.
Abstract Classes vs Interfaces
Both define contracts. Abstract classes can hold state and partial implementation; interfaces define capabilities a class can implement.
SOLID Principles
Five principles for maintainable, extensible object-oriented design.
Design Patterns
Reusable solutions to common design problems, grouped into creational, structural and behavioural patterns.
Low-Level Design Basics
LLD interviews ask you to model classes, relationships and interactions for systems like a parking lot or library.
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