AS Level Computer Science 9618 Notes
Free, detailed, exam-focused notes for every topic in the Cambridge International AS Level Computer Science 9618 syllabus (for exams from 2026), covering both Paper 1: Theory Fundamentals and Paper 2: Fundamental Problem-solving and Programming Skills, with worked examples, exam-style practice questions, and interactive tools built to make the harder ideas click.
Cambridge International AS Level Computer Science 9618 is assessed across two written papers for the AS Level qualification: Paper 1 (Theory Fundamentals) and Paper 2 (Fundamental Problem-solving and Programming Skills). This hub links to a complete set of notes for every syllabus section examined in both papers, rebuilt from the ground up to be genuinely exam-thorough rather than a bare summary, with worked examples, practice questions, and interactive tools for the concepts that are hardest to picture from text alone: logic circuits, the Fetch-Execute cycle, encryption, normalisation, and more.
All AS Level 9618 Chapters
Chapters 1 to 8 cover everything examined in Paper 1: Theory Fundamentals. Chapters 9 to 12 are combined into a single page covering everything examined in Paper 2: Fundamental Problem-solving and Programming Skills. Each page is self-contained, so you can jump straight to the topic you need.
Number systems and data representation from the ground up: binary, hexadecimal and two's complement arithmetic, how images and sound are digitised, and lossy versus lossless compression.
How devices talk to each other: network topologies and hardware, the protocols that make the internet work, and how data is broken into packets and reassembled.
The physical building blocks of a computer system, plus Boolean logic and logic circuits, with an interactive logic gate explorer to test truth tables yourself.
What actually happens inside the CPU: the Fetch-Execute cycle stepped through one register at a time, assembly language addressing modes, and bitwise operations.
What an operating system actually manages behind the scenes, and how compilers, interpreters and assemblers turn source code into something a processor can run.
Threats to data and the defences against them: authentication, firewalls, symmetric and asymmetric encryption, and the checks that keep data accurate.
The professional and legal side of computing: codes of conduct, copyright and intellectual property, open-source licensing, and the impact of artificial intelligence on society.
How relational databases are structured and normalised, what a DBMS actually does, and how to read and write SQL, including joins and aggregate functions.
Paper 2 territory: computational thinking and algorithm design in pseudocode, data structures like arrays and files, structured programming constructs, and the program development life cycle.
Exam Structure: Paper 1 & Paper 2
AS Level Computer Science 9618 is assessed by two written components, each worth 50% of the AS Level grade. Neither paper needs a computer during the exam itself, Paper 4 (the practical programming paper) only exists at full A Level.
- Assesses syllabus sections 1 to 8
- Written paper, externally assessed
- Candidates answer all questions
- Covered by chapters 1 to 8 on this site
- Assesses syllabus sections 9 to 12
- Written paper, answers given in pseudocode
- Candidates answer all questions
- Covered by the combined chapters 9-12 page
Assessment objectives
Cambridge weights every 9618 paper against three assessment objectives. Knowing the split helps you judge where marks actually come from: AO1 questions test recall, AO2 tests application, and AO3 tests design, programming and evaluation, which is why Paper 2 leans so heavily on AO3.
| Assessment objective | What it tests | Weighting in AS Level |
|---|---|---|
| AO1 | Knowledge and understanding of computer science principles and concepts | 30% |
| AO2 | Applying that knowledge, including analysing problems in computational terms | 40% |
| AO3 | Designing, programming and evaluating computer systems, and making reasoned judgements | 30% |
How to Use These Notes
These notes are built to be read once for understanding and then returned to for revision, not skimmed once and forgotten. A few ways to get more out of them.
Work through the interactive tools, not just the text
Several ideas in this syllabus are much easier to understand as something you manipulate than as something you read about. Every chapter includes interactive tools built specifically for its hardest concepts, a logic gate explorer in Chapter 3, a step-through Fetch-Execute cycle in Chapter 4, an encryption diagram in Chapter 6, a normalisation stepper in Chapter 8, and more. Use them before moving on, not after.
Use the worked examples as a template
Every chapter includes fully worked examples showing the exact steps examiners expect to see, not just the final answer. When you hit a practice question, try it yourself first, then compare your working line by line against the nearest worked example.
Answer every practice question before revealing the model answer
Each chapter ends with exam-style practice questions and model answers. Cover the answer, write your own response as if it were the real exam, and only then check it. This is a far better test of what you actually know than reading the model answer straight away.
Revise Paper 1 and Paper 2 differently
Paper 1 rewards precise recall and clear explanation, so flashcard-style repetition of definitions and diagrams pays off. Paper 2 rewards the ability to actually write and trace pseudocode under time pressure, so the best preparation is writing algorithms by hand, not just reading them.
Frequently Asked Questions
9618 is the syllabus code for Cambridge International AS & A Level Computer Science, set by Cambridge Assessment International Education. The AS Level covers the first half of the full qualification and is assessed by two papers: Paper 1 (Theory Fundamentals) and Paper 2 (Fundamental Problem-solving and Programming Skills). Exams are available in the June and November series each year.
Two, if you are taking AS Level only. Paper 1 (Theory Fundamentals, 1 hour 30 minutes, 75 marks) and Paper 2 (Fundamental Problem-solving and Programming Skills, 2 hours, 75 marks), each worth 50% of the AS Level grade. Papers 3 and 4 only apply if you continue on to the full A Level.
Twelve syllabus sections in total: information representation, communication, hardware, processor fundamentals, system software, security and data integrity, ethics and ownership, and databases for Paper 1, then algorithm design and problem-solving, data types and structures, programming, and software development for Paper 2. Every section has its own chapter on this site.
AS Level is a standalone qualification covering sections 1 to 12 and assessed by Paper 1 and Paper 2. The full A Level continues on to sections 13 to 20, adding Paper 3 (Advanced Theory) and Paper 4 (a hands-on Practical programming exam), each worth 25% of the A Level grade. Many students take AS Level in one year and carry the result forward into A Level the next.
No. Paper 2 answers are written in Cambridge's own pseudocode style, not in any particular language, so there is no syntax to memorise beyond the pseudocode conventions themselves. That changes at full A Level, where Paper 4 requires actual code in Java, VB.NET or Python.
Yes, every chapter on this site is free to read, with no sign-up required.
Work through each chapter's interactive tools until the underlying mechanism actually makes sense, not just the definition, then close the page and try to reconstruct the worked examples from memory. Finish with the practice questions at the end of each chapter, answering in full before checking the model answer.
Official past papers and mark schemes are distributed through Cambridge International's School Support Hub, which your school's exams officer can give you access to. These notes are designed to build the understanding you need before attempting past papers, not to replace them.
