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Computer Science.
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Computer Science rewards students who can decompose a problem, dry-run it on paper, and then explain the machine underneath. These guides start with the idea you can retrieve in an exam, then pin it to a worked trace, a diagram or a precise definition the mark scheme actually uses.
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Open guideAlgorithms and programming
Algorithms and programming
made memorable.
Computational thinking, core constructs, and the logic that sits under every IF and WHILE.
All Algorithms and programming revisionAlgorithms
Decomposition, abstraction, searching, sorting, and how to prove an algorithm works with a trace table.
Programming basics
Sequence, selection, iteration, data types, strings, arrays, functions, validation and the three faces of errors.
Boolean logic
AND, OR and NOT gates, truth tables, and how to read a logic circuit the way the paper draws it.
Trace tables
GCSE Computer Science trace tables: one column per variable, one line of the algorithm at a time, and the off-by-one errors that drop the last output mark.
Linear search
GCSE Computer Science linear search: check each item in order, works on unsorted lists, worst case n comparisons, and when it is the right algorithm to name.
Binary search
GCSE Computer Science binary search: the list must be sorted, each step halves the search space, and a full midpoint trace is how you prove it.
Bubble sort
GCSE Computer Science bubble sort: compare neighbouring pairs, swap if they are out of order, use a flag or a shrinking tail, and trace a four-item list.
Merge sort
GCSE Computer Science merge sort: split the list to one-item pieces, merge sorted halves back together, and compare time and extra memory with bubble sort.
Sequence, selection and iteration
GCSE Computer Science programming constructs: sequence, IF selection, WHILE and FOR iteration, and how nested decisions and loops are read in exam algorithms.
Arrays and lists
GCSE Computer Science arrays and lists: indexing from 0 or 1, bounds, iteration through items, and the out-of-range errors that crash a dry-run.
Subroutines and functions
GCSE Computer Science subroutines and functions: parameters, return values, local versus global variables, and why reuse beats copy-paste in exam code.
SQL SELECT queries
GCSE Computer Science SQL: SELECT, FROM and WHERE, the difference between = and LIKE, and how to write a query that actually matches the table in the paper.
High-level and low-level languages
GCSE Computer Science high-level versus low-level languages: abstraction, portability, assembly, machine code, and when each level is chosen.
Decomposition and abstraction
GCSE Computer Science decomposition and abstraction: break problems into sub-problems, hide detail behind interfaces, and design algorithms at the right level.
Robust testing
GCSE Computer Science robust testing: normal, boundary and erroneous data, test plans, expected versus actual, and why testing cannot prove zero bugs.
Computer systems and networks
Computer systems and networks
made memorable.
What the CPU actually does, and how machines share data without chaos.
All Computer systems and networks revisionNetworks
LANs and WANs, hardware, topologies, protocols, DNS and the factors that make a network fast, reliable or neither.
Systems architecture
The CPU’s fetch–decode–execute cycle, what actually speeds a processor up, memory versus storage, and embedded systems.
The fetch–decode–execute cycle
GCSE Computer Science fetch–decode–execute: how the PC, MAR, MDR, CIR and ALU move one instruction from memory through the CPU, every cycle.
Von Neumann architecture
GCSE Computer Science Von Neumann architecture: stored program, shared memory for instructions and data, and the bottleneck that comes from one bus doing both jobs.
TCP/IP layers
GCSE Computer Science TCP/IP: application, transport, internet and network-access layers, what each one is for, and how a packet is passed down and back up the stack.
Compilers and interpreters
GCSE Computer Science compilers and interpreters: translate high-level code to machine code, compile-time versus run-time translation, and when each translator is used.
Input and output devices
GCSE Computer Science input and output devices: sensors, keyboards, touchscreens, monitors, actuators, printers — data flow into and out of the CPU.
Network hardware
GCSE Computer Science network hardware: router, switch, hub, wireless access point, NIC, modem — roles in LAN, WAN and the internet.
Data representation and security
Data representation and security
made memorable.
Binary, images, sound, and the threats that turn data into an incident.
All Data representation and security revisionBinary and data representation
From bits and overflow to hex, characters, images, sound and why compression has to throw information away — or not.
Cyber security
How systems are actually attacked — malware, people and weak configuration — and the controls that make an attack expensive.
Binary and hexadecimal conversion
GCSE Computer Science binary and hex: group bits into nibbles, digits 0–9 and A–F, and a full conversion of 156 into hexadecimal with the binary in the middle.
Logic gates and truth tables
GCSE Computer Science logic gates: AND, OR, NOT and XOR, how to fill a truth table including a 3-input circuit, and how to turn English into gates.
Types of malware
GCSE Computer Science malware: virus, worm, trojan, spyware, ransomware — how each spreads, what damage it does, and basic prevention.
Ethical and legal issues in CS
GCSE Computer Science ethics and law: data protection, copyright, software licences, Computer Misuse Act, and professional responsibility.
Privacy and cyber security
GCSE Computer Science privacy and security: threats, encryption, authentication, and the human layer beyond firewalls.
Secondary storage
GCSE Computer Science secondary storage: HDD, SSD, optical, magnetic tape, cloud — capacity, speed, durability and cost trade-offs.
Sound representation
GCSE Computer Science sound: sampling rate, bit depth, file size calculation, and analogue-to-digital conversion.
Image representation
GCSE Computer Science images: pixels, resolution, colour depth, file size, metadata and compression.
Environmental impact of computing
GCSE Computer Science environmental impact: e-waste, energy use, rare earths, cloud data centres, and sustainable practice.
Built for real revision
GCSE Computer Science,
without the waffle.
GCSE Computer Science revision for algorithms, programming, binary, networks, cyber security, systems architecture and Boolean logic — with trace tables, not hand-waving.
34 guides, each with a memory hook, precise knowledge, a worked example and a retrieval check. Use a page for a quick refresh before exam questions, or as the first step in a spaced revision session.