Educate in CS

For students, teachers, and self-learners.

Whether you're just starting out or brushing up on a tricky topic, you're in the right place. Free notes, worked examples, and interactive exercises — from how hardware works to writing your first sorting algorithm. Currently aligned with IB CS (2027). Code examples use Java.

Browse all topics

108

topic pages

5

quiz formats

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The big picture

Every computer does the same four things

It takes input, runs a process, produces output, and saves to storage. You type on a keyboard (input), the CPU runs instructions (process), the screen shows results (output), and files are saved to disk (storage). Every topic on this site zooms into one part of this cycle.

Topics

Pick where you'd like to start

Each topic has notes, worked examples, interactive exercises, and a teacher guide. Organised by the six layers of the IB CS 2027 syllabus, plus cross-cutting topics.

Information Layer

Information

How numbers, text, images, audio, and video are encoded as binary.

3 pages

Hardware Layer

Hardware

The CPU fetches, decodes, and executes — billions of times per second. Memory, cache, logic gates, GPU, storage.

9 pages

Programming Layer

Java Fundamentals

Variables, data types, operators, Strings, exception handling, debugging.

5 pages

Programming Constructs

Sequence, selection, iteration, methods — the three building blocks of every program.

4 pages

Data Structures

1D and 2D arrays, ArrayLists, stacks, queues — choosing the right collection.

6 pages

Algorithms

Searching, sorting, and Big-O notation — picking the right tool for the job.

6 pages

OOP & Java

Modelling problems as interacting objects — classes, encapsulation, inheritance, polymorphism.

26 pages

File Processing

Reading and writing text files in Java — Scanner, BufferedReader, FileWriter.

3 pages

Abstract Data Types

Building structures from scratch — linked lists, stacks, queues, BSTs, hash tables.

11 pages · HL

Operating Systems Layer

Operating Systems

Scheduling, multitasking, interrupts — how the OS juggles programs and devices.

6 pages

Applications Layer

Databases

How databases store and query structured data — relations, SQL, normalisation.

Coming soon

Machine Learning

How machines learn from data — supervised learning, neural networks, training.

Coming soon

Communication Layer

Networks

Packets, protocols, architectures, encryption — how devices talk to each other.

7 pages

Also on the site

Computational Thinking

Decomposition, abstraction, pattern recognition — the thinking that comes before coding.

4 pages

Ethics & Implications

Privacy, intellectual property, social impact — the responsibilities that come with computing.

Coming soon

IB CS Assessments

Internal Assessment

The 30-mark IB CS project — criteria, planning, development, evaluation.

8 pages

Case Study

HL Paper 3 — the annual case study, applied concepts, and structured response strategies.

Coming soon

CS Extended Essay

A 4,000-word independent research essay in computer science — choosing a topic, framing a question, evaluating sources.

7 pages

What you'll find on each page

Five ways to practise

✓ Adjacent elements

First and last

Multiple choice

Pick the right answer; see why each option is or isn't correct.

i   j   arr[j]

0   0   5

0   1   _

Trace tables

Step through code line-by-line; fill in variable values; check each row.

for (int i = 0;

     i < n;

     i__) {

Code completion

Fill the blanks in a method or loop until the code works.

for (int i = 0; i <=

   arr.length; i++)

  sum += arr[i];

Spot the bug

Find the broken line; pick the fix that makes the test pass.

x = 5

x *= 2

print(x)

→ 10

Predict output

Read the code, write what it prints, hit check.

And on every content page

More than just quizzes

• Key Conceptsclear explanations with precise terminology
• Worked Examplesstep-by-step solutions
• Practice ExercisesCore, Extension, and Challenge levels
• Glossary Tooltipshover over highlighted terms for a quick definition
• Connectionsprerequisites and related topics to explore next
• GitHub Classroomprogramming pages include assignments with automated tests