CS Core Subjects

Every abstraction in modern software is built on top of a core CS subject. When your React app slows to a crawl, you debug it with knowledge of how browsers handle the JavaScript event loop — Operating Systems. When your SQL query takes 30 seconds, you fix it with knowledge of B-tree indexes — DBMS. When a packet drops during a video call, you understand why using knowledge of TCP congestion control — Computer Networks. Core subjects are not academic exercises. They are the conceptual infrastructure beneath every tool and framework you will ever use.

In India, core subjects are also the primary focus of GATE CS, university examinations, and technical interviews at product companies. A student who deeply understands OS scheduling, relational algebra, and finite automata can reason through unfamiliar problems from first principles — the most prized skill in any engineering interview. Learn with LSGP treats these five subjects as the foundation of everything else in the CS curriculum.

An Operating System (OS) is the master program that manages all hardware and software resources on a computer. It acts as the middleman between your applications and the bare hardware — so when you write open("file.txt") in Python, it is the OS that actually talks to the disk controller. Understanding how an OS works transforms you from a developer who uses abstractions to an engineer who understands what lies beneath them.

🎬 Process State Diagram (Animated)

CPU Scheduling — Gantt Chart (Animated)

The OS scheduler decides which process gets the CPU at any moment. Below is a Round Robin schedule (time quantum = 2) for four processes: P1(burst=4), P2(burst=3), P3(burst=5), P4(burst=2).

Key OS Topics

📺 Recommended Video — Process Synchronisation

A Database Management System is software that manages organised collections of data, providing interfaces for storing, retrieving, and manipulating it reliably. Every application that stores data — banking apps, social networks, government portals, EdTech platforms like Learn with LSGP — uses a database. Understanding DBMS teaches you not just how to write SQL, but why relational databases are designed the way they are: to eliminate redundancy, maintain consistency, and support concurrent access at scale.

📊 ER Diagram — Student Enrolment Database

Normalisation — 1NF to BCNF

SQL — The Language of Relational Data

-- Find students enrolled in more than 2 courses
SELECT s.name, COUNT(e.course_id) AS total
FROM students s
JOIN enrolments e ON s.id = e.student_id
GROUP BY s.id, s.name
HAVING COUNT(e.course_id) > 2;

-- Find courses with no enrolments (left join pattern)
SELECT c.title
FROM courses c
LEFT JOIN enrolments e ON c.id = e.course_id
WHERE e.course_id IS NULL;

-- Relational algebra: π(name)(σ(level='beginner')(courses))
-- Same as: SELECT name FROM courses WHERE level = 'beginner';

📺 Recommended Video — Normalisation

Computer Networks is the study of how data moves between computers — from the physical signals on a wire to the protocols that ensure your video call does not turn into garbled noise. Every piece of software you write that communicates with another machine, an API, a database, or the internet — uses the protocols and principles you study here. Understanding networks makes you a better backend developer, a better systems engineer, and a much more effective debugger of production issues.

🎬 OSI Model — Interactive Layer Stack

Hover over each layer to highlight it and see which protocols operate there.

TCP vs UDP

📺 Recommended Video — Subnetting

A compiler translates source code written in a high-level language (like C or Java) into machine code that the CPU can execute. The process is not a single step — it is a pipeline of six distinct phases, each transforming the program into a progressively lower-level representation. Understanding compilers reveals what is happening when you write int x = a + b * 2; — how the compiler parses it, checks types, optimises it, and ultimately generates the machine instructions that run on your CPU.

📊 Compilation Pipeline — Flowchart

Parsing — Top-Down vs Bottom-Up

📺 Recommended Video — LL(1) Parsing

Theory of Computation (TOC) answers the most fundamental question in computer science: what can a computer compute, and what are its fundamental limits? This is not about the speed of your laptop or the size of your RAM — it is about what is theoretically computable at all, regardless of resources. TOC is the most abstract of the core subjects, but also the most intellectually beautiful. Its results — like the undecidability of the Halting Problem — are among the deepest theorems in all of mathematics.

📊 DFA — Accepts strings ending in '01'

The Chomsky Hierarchy

Decidability — What Computers Cannot Do

📺 Recommended Video — Finite Automata

Core CS subjects are best studied in a specific order that builds on conceptual dependencies. Learn with LSGP recommends the sequence below for students targeting GATE, university examinations, or technical interviews simultaneously.

Recommended Study Sequence

Study Methods That Actually Work