A Level Computer Science (9618) Notes

Every chapter of the computer science syllabus for Cambridge A Level 9618, in the order the book takes them. 38 chapters have a finished lesson — notes, worked examples, a graph you can move, flashcards and a quiz. The rest are mapped and being written.

Also called AS Level, Cambridge A Level, CAIE A Level.

01

Information representation

▸Number SystemsWhy a machine that only knows two symbols can represent anything · 20 min · 8 questions→▸Text, Sound and ImagesHow a machine that stores only numbers holds a photograph · 20 min · 8 questions→▸Data Storage and CompressionMaking files smaller, and deciding what you can afford to lose · 18 min · 8 questions→

02

Communication

▸Computer NetworksHow a message crosses the world in fragments and arrives whole · 22 min · 6 questions→▸The Internet and the World Wide WebTwo different things, and what actually happens when you type an address · 18 min · 8 questions→

03

Hardware

▸Introduction to SystemsWhat is actually inside the box, and how it runs a program · 20 min · 8 questions→▸Input and Output DevicesGetting data in and results out, and choosing the right device for the job · 18 min · 8 questions→▸Data Storage and Virtual MemoryThree technologies, and the trick that lets a machine run more than it can hold · 18 min · 8 questions→▸Digital Systems and Logic DesignGates, truth tables, and building arithmetic out of switches · 20 min · 8 questions→

04

Processor Fundamentals

▸CPU Architecture and Parallel ProcessingWhat is inside the processor, and why one instruction takes several steps · 26 min · 8 questions→▸Assembly Language and Bit ManipulationOne instruction per line, and the operations that work on individual bits · 24 min · 8 questions→

05

System Software

▸Operating Systems: Structure and ServicesThe program that makes every other program possible · 20 min · 8 questions→▸Translators and CompilationTurning source you can read into instructions a processor can run · 22 min · 8 questions→

06

Security, privacy and data integrity

▸Cyber SecurityThe threats named in the syllabus, and the specific defence against each · 20 min · 8 questions→▸EncryptionMaking intercepted data useless, and why the method being public does not matter · 18 min · 8 questions→▸Methods of Error DetectionNoticing that data arrived wrong, and sometimes fixing it · 18 min · 8 questions→

07

Ethics and Ownership

▸Ethical, Social and Legal Concerns in Computer UsageWhat you are allowed to do, what you should do, and why they differ · 18 min · 8 questions→

08

Databases

▸Basic Concepts and Terminologies of DatabasesKeys, relationships and the software that holds it all together · 20 min · 8 questions→▸Database Design ProcessFrom a description in words to a set of tables that will not fight you later · 20 min · 8 questions→▸Data Integrity and NormalizationRemoving the duplication that lets a database contradict itself · 22 min · 8 questions→▸SQL: Defining and Querying a DatabaseTwo sublanguages — one builds the tables, the other asks them questions · 24 min · 8 questions→

09

Algorithm Design and Problem-solving

▸Computational ThinkingBreaking a problem down until every piece is something you can actually do · 20 min · 8 questions→▸Algorithms & Big-OSorting, searching, and measuring cost honestly · 22 min · 6 questions→

10

Data Types and Structures

▸Data BasicsWhat data is, how it is stored, and why files stopped being enough · 18 min · 8 questions→▸Data StructuresArrays, lists, stacks, queues, trees · 24 min · 6 questions→▸File Handling in CMaking data outlive the program that created it · 18 min · 8 questions→

11

Programming

▸Introduction to Python ProgrammingVariables, types, input and output — the whole vocabulary of a first program · 20 min · 8 questions→▸Control Structures in PythonChoosing, repeating, and knowing which loop the problem needs · 20 min · 8 questions→▸Functions in CBreaking a program into pieces, and what a function can and cannot change · 20 min · 8 questions→

12

Software Development

▸Introduction to Software DevelopmentThe stages between an idea and working software, and why skipping one is expensive · 20 min · 8 questions→

13

Data Representation (A Level)

▸Floating-Point RepresentationTrading precision for range, and why 0.1 cannot be stored exactly · 24 min · 8 questions→

14

Communication and internet technologies

▸Computer NetworksHow a message crosses the world in fragments and arrives whole · 22 min · 6 questions→▸Types and Methods of Data TransmissionPackets, wires and directions — how data actually gets from one machine to another · 18 min · 8 questions→

15

Hardware and Virtual Machines

▸CPU Architecture and Parallel ProcessingWhat is inside the processor, and why one instruction takes several steps · 26 min · 8 questions→▸Boolean Algebra and Logic CircuitsSimplifying a circuit on paper before building it in silicon · 24 min · 8 questions→

16

System Software (A Level)

▸Operating Systems: Structure and ServicesThe program that makes every other program possible · 20 min · 8 questions→▸Translators and CompilationTurning source you can read into instructions a processor can run · 22 min · 8 questions→

17

Security (A Level)

▸EncryptionMaking intercepted data useless, and why the method being public does not matter · 18 min · 8 questions→

18

Artificial Intelligence (AI)

▸Introduction to Artificial Intelligence and Machine LearningWhat it means for a program to learn from data instead of being told the rules · 20 min · 8 questions→▸Applications of Artificial IntelligenceWhere AI is genuinely used, what it is worth, and what it costs · 18 min · 8 questions→

19

Computational thinking and Problem-solving

▸Algorithms & Big-OSorting, searching, and measuring cost honestly · 22 min · 6 questions→▸RecursionA routine that calls itself, and the stack that makes it possible · 22 min · 8 questions→

20

Further Programming

▸Programming Paradigms and Exception HandlingFour ways of describing a computation, and what to do when it goes wrong · 24 min · 8 questions→▸Object-Oriented ProgrammingFour ideas that organise large programs · 18 min · 6 questions→