Pearson Edexcel · A Level · 9CS0
Computer Science — Keywords & Key Terms — Definitions Glossary (2026)
Pearson Edexcel A Level Computer Science (9CS0)
Topic-by-topic keywords, key terms and definitions for precise exam language—separate from our revision checklists (topic coverage) and formula sheets (equations).
Keywords & Key Terms — definitions
Examiner-style keywords and definitions organised by syllabus topic. Terms are tagged Essential (start here), Core (typical exam standard), and Advanced for harder distinctions — tick each row when you can recall it. Your progress is saved in this browser for this list.
Pearson Edexcel A Level Computer Science (9CS0)
Pearson Edexcel A Level Computer Science (9CS0)
Pearson Edexcel A Level Computer Science (9CS0)
Pearson Edexcel 9CS0 (2026) covers principles of computer science (Paper 1) and application of computational thinking (Paper 2), with a programming project — assessing theoretical computer systems alongside algorithmic problem-solving and software development.
Mark schemes: Pearson rewards linked reasoning that moves from technical definition to consequence (e.g. 'cache reduces latency BECAUSE it sits closer to the CPU SO fewer cycles are wasted fetching from RAM'). Big-O answers must state the complexity class and justify it from the loop structure. Boolean simplification must show each law named (De Morgan, distribution) at the step it is applied.
Active recall: 0 / 20 terms ticked
| Recalled | Topic | Level | Keyword | Definition |
|---|---|---|---|---|
| Computer architecture & hardware | Essential | Von Neumann architecture | Single shared memory and bus storing both program instructions and data sequentially. | |
| Computer architecture & hardware | Core | Fetch–decode–execute cycle | Repeated CPU process retrieving, interpreting, and carrying out each instruction. | |
| Computer architecture & hardware | Core | CPU registers | Fast on-chip stores: PC, MAR, MDR, CIR, ACC each with a defined role. | |
| Computer architecture & hardware | Core | Memory hierarchy | RAM is volatile working memory, ROM is non-volatile firmware, cache speeds frequent access. | |
| Computer architecture & hardware | Advanced | RISC vs CISC | RISC uses few simple fixed-length instructions, CISC uses many complex variable-length ones. | |
| Algorithms & data structures | Core | Big-O notation | Worst-case time growth: O(1), O(log n), O(n), O(n log n), O(n²). | |
| Algorithms & data structures | Core | Search algorithms | Linear scans every element O(n), binary halves a sorted list giving O(log n). | |
| Algorithms & data structures | Core | Sorting algorithms | Bubble O(n²), merge O(n log n) divide-and-conquer, quicksort average O(n log n) using a pivot. | |
| Algorithms & data structures | Advanced | Graph traversal | Dijkstra's finds shortest weighted paths; BFS uses queues, DFS uses stacks. | |
| Algorithms & data structures | Core | Abstract data structures | Stacks, queues, lists, hash tables, trees, and graphs organise data logically. | |
| OOP & paradigms | Essential | Encapsulation | Bundling attributes and methods inside a class while hiding internal state from outside code. | |
| OOP & paradigms | Core | Inheritance | A subclass derives attributes and methods from a parent class, extending or overriding them. | |
| OOP & paradigms | Core | Polymorphism | A single interface or method name behaves differently depending on the object type. | |
| OOP & paradigms | Advanced | Functional programming | Stateless evaluation of pure functions using first-class functions and immutability. | |
| OOP & paradigms | Advanced | Declarative paradigm | Programmer specifies what result is required, not the step-by-step procedure. | |
| Data representation & networks | Core | Two's complement | Standard signed binary representation where the most significant bit carries negative weight. | |
| Data representation & networks | Advanced | IEEE 754 floating point | Standard format storing sign, biased exponent, and normalised mantissa for real numbers. | |
| Data representation & networks | Core | TCP/IP layers | Four-layer stack — application, transport, internet, link — handling end-to-end communication. | |
| Data representation & networks | Core | Encryption | Symmetric uses one shared key, asymmetric uses a public–private key pair as in RSA. | |
| Data representation & networks | Advanced | Boolean algebra & De Morgan | Logic simplification using De Morgan's laws, distribution, and absorption rules. |
Pair this with our revision checklists, formula sheets hub and past paper finder.
Computer Science (9CS0) — Keywords & Key Terms FAQ
- What is on this Pearson Edexcel A Level Computer Science keywords and key terms list?
- It is a topic-organised glossary of important computer science terms with short, exam-style definitions aligned to Pearson Edexcel A Level Computer Science (9CS0) (9CS0). It is designed for “define”, “state”, “outline” and “explain” questions where precise vocabulary earns marks.
- How should I use this Computer Science glossary alongside past papers?
- Tick terms when you can recall them without reading the answer, then check your wording against mark schemes. Pair vocabulary practice with past papers for A Level Computer Science (9CS0) so you apply terms in context.
- Is this the same as a revision checklist or a formula sheet?
- No. Revision checklists help you track which syllabus topics you have covered and your confidence—separate pages on Tutopiya. Formula sheets summarise equations and quantitative relationships. This page is only a definitions and key-terms glossary for Computer Science.
- Can I download this Computer Science keywords and key terms list for free?
- Yes. After a quick free sign-up you can download a UTF-8 CSV (opens in Excel or Google Sheets) or open a print-friendly page and save as PDF. Browsing the list on the page is free.
- Is this Computer Science list aligned to the 9CS0 specification?
- Topic groupings and wording follow Pearson Edexcel A Level Computer Science (9CS0) for Pearson Edexcel A Level. Always confirm final learning objectives and any regional options in your official specification and recent examiner reports for your exam session.
- Why focus on definitions instead of full notes?
- Mark schemes reward correct technical terms and clear links between ideas. A compact glossary lets you drill the exact language examiners expect for Computer Science at A Level, separate from longer notes or topic trackers.