GCSE Computer Science
Understanding the fundamental architecture of computer systems.
Learn about the CPU, its components (ALU, control unit, cache), and how it processes instructions. Explore the fetch-decode-execute cycle, different types of processors, and factors affecting CPU performance.
This unit covers the Von Neumann architecture, embedded systems, and how hardware components work together to run software.
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Your phone can do 11 trillion calculations every second—more than every human who has ever lived could do in their entire lifetimes, combined. How is that even possible?
Display comparison: Apollo 11 guidance computer (0.043 MHz, 2KB RAM) vs iPhone (3.23 GHz, 6GB RAM). Ask students to guess how many times more powerful—reveal it's roughly 100,000x. Show video of moon landing and ask: 'If they landed on the moon with THAT, what could we do with THIS?' Let students brainstorm applications that require massive computing power (AI, games, video editing, simulations). Introduce the question we'll answer: What makes modern CPUs so incredibly fast?
Resources:
Visual showing specs side-by-side with visual representations of the difference in power
30-second clip of Eagle landing, emphasising the computer guidance
Teacher Notes:
Let students speculate wildly. Accept all answers. The goal is to create genuine wonder. If students mention gaming or AI, these are perfect hooks for later lessons.
Core teaching video covering: (1) The CPU as the 'brain'—it processes instructions and makes decisions, (2) The fundamental job: fetch an instruction, work out what it means, execute it, repeat, (3) Introduction to ALU as the 'calculator' that does all arithmetic and logic, (4) Introduction to CU as the 'manager' that coordinates everything. Use animation to show instructions flowing in and results flowing out.
Resources:
Animated explainer with real CPU footage, showing physical chips alongside diagrams
Key points document with diagrams students can annotate
Teacher Notes:
Pause video at key points for classroom discussion. Ask: 'What do you think happens next?' before revealing each component.
Physical/digital simulation activity. In classroom: Students take roles—one is CU (reads instruction cards aloud), one is ALU (has calculator, does maths), one is Memory (holds number cards), others are the 'data bus' passing information. Work through a simple program: LOAD 5, LOAD 3, ADD, STORE. Online version: Interactive simulation where students drag instructions through CPU components. Debrief: What happened? What problems did you encounter? Why is coordination important?
Resources:
Printable cards for each role with clear responsibilities
Simple program written as individual instruction cards
Browser-based interactive simulation for remote learners
Teacher Notes:
Expect chaos the first time—that's the point! Let them fail, then discuss why it was hard. This builds appreciation for what the CPU does billions of times per second.
Students read illustrated material explaining the three stages: FETCH (get the next instruction from memory), DECODE (CU works out what the instruction means), EXECUTE (carry out the instruction, often using ALU). Include diagram showing the cycle as a loop. Students annotate or complete a cloze exercise.
Resources:
Visual walkthrough with everyday analogies (chef following recipe, assembly line worker)
Blank/partial diagram for students to label
Teacher Notes:
Emphasise that this cycle happens BILLIONS of times per second. The repetition and speed is what gives CPUs their power.
Show brief, engaging content about: Why Apple left Intel, what 'nanometer' means in chip manufacturing, the global shortage of chips in 2021-2023 and why it affected PlayStation stock. Mention ARM's Cambridge headquarters and UK chip design careers. Optional: Show salary ranges for chip designers to illustrate career potential.
Resources:
3-minute engaging summary of the semiconductor industry
Brief on UK's role in global chip design
Teacher Notes:
Keep this light and inspiring. Goal is 'wow, this stuff actually matters and people get paid to work on it.' Connect to games consoles and phones students own.
Multi-choice quiz covering: What is the CPU's job? What does ALU stand for? What does the Control Unit do? Put these in order: Execute, Fetch, Decode. Wrong answers link to specific review content. Followed by discussion: What questions do you still have? What would you like to know more about?
Resources:
Interactive quiz with branching feedback
Short explanations for each common misconception
Teacher Notes:
Use quiz results to identify students who need support. Note common wrong answers for class-wide clarification next lesson.
Explore how Apple shocked the industry by designing their own M-series chips, and why companies like NVIDIA, AMD, and Intel are in a constant race. Show how chip design affects the devices students use daily—from gaming performance to battery life on their phones.
Connection: Understanding that CPU architecture is a real competitive battleground helps students see why we study these components—engineers earning six-figure salaries are working on exactly these problems right now.
Further Reading:
ARM Holdings in Cambridge designs the architecture for 99% of all smartphones on Earth. Discuss how a British company became the foundation of mobile computing and why this matters for UK tech careers.
Connection: Links CPU architecture knowledge to local career opportunities and shows the UK's significant role in global computing.
Further Reading:
Support:
Stretch:
https://visual6502.org/ - See a real CPU in action
Why does your computer have so many different types of memory? And why can't it just use one really fast one for everything?
Present the puzzle: Modern CPUs can execute billions of instructions per second, but RAM can only deliver data millions of times per second. Show the mismatch visually—CPU asking for data and waiting, waiting, waiting... Ask: 'If you were designing a computer, how would you solve this problem?' Collect ideas. Reveal that computer scientists solved this with 'cache'—a small, super-fast memory right next to the CPU.
Resources:
Visual showing CPU vs RAM speed disparity
Scaffolded questions for group discussion
Teacher Notes:
Students might suggest: make RAM faster, slow down CPU, use prediction. All valid ideas! The real solution uses a bit of several approaches.
Core teaching video covering: (1) Registers—tiny storage locations INSIDE the CPU for immediate work, like the numbers you're adding right now, (2) Cache—small but fast memory that predicts what data you'll need next, (3) The memory hierarchy concept—faster is more expensive and smaller, (4) Analogy: Desk (registers) → Drawer (cache) → Filing cabinet (RAM) → Warehouse (storage). Include real CPU die photos showing cache taking up significant chip space.
Resources:
Animated explainer with physical chip imagery
Printable pyramid showing speed/size trade-offs
Teacher Notes:
The desk/drawer analogy is powerful. Ask: What do you keep on your desk? Why? Same principle as cache—keep frequently used things close.
Scenario-based activity. Students are given a 'budget' of speed-points and capacity-points and must design a memory system for different use cases: (1) Gaming PC, (2) Video editing workstation, (3) Budget laptop. They must decide: How much cache? How many registers? How much RAM? Justify decisions. Groups present their designs and explain trade-offs. Online version: Interactive calculator showing performance implications.
Resources:
Printable planning sheet with budget constraints
Cards describing each computer's intended use
Interactive tool for remote learners
Teacher Notes:
There's no single 'right' answer—that's the point. Real computer designers face these trade-offs. Encourage debate between groups.
Focused reading on registers: What they are (tiny, ultra-fast storage inside CPU), why we need them (CPU can't do maths on data in RAM directly—must load into registers first), types we'll explore next lesson (MAR, MDR, PC, Accumulator mentioned as preview). Students complete matching activity: register characteristic → explanation.
Resources:
Illustrated guide with CPU diagram showing register location
Interactive or printable matching exercise
Teacher Notes:
Emphasise that registers are INSIDE the CPU—draw on previous lesson's CPU diagram. Preview that next lesson we'll learn about specific register types.
Game-based learning activity. Students play a 'cache simulator' where they must predict what data to keep in limited cache slots. CPU requests data; if it's in cache (HIT) = fast, if not (MISS) = slow. Track their hit rate percentage. Discuss: What strategies worked? What is the computer doing automatically that you had to do manually? Introduce 'cache hit rate' as a performance metric.
Resources:
Browser-based interactive game
Reflection questions on caching strategies
Teacher Notes:
Students often discover LRU (Least Recently Used) strategy on their own. Name it for them when they describe it.
Quiz covering: What is cache? Why is it faster than RAM? What are registers? Why can't we just have loads of cache? Branching feedback for wrong answers. Tease next lesson: 'We know CPUs have registers—but what are they called and what do they do? Next time, we'll meet MAR, MDR, the Program Counter, and the Accumulator.'
Resources:
Interactive quiz with targeted feedback
Brief preview graphic showing register names
Teacher Notes:
The teaser should create curiosity about the specific registers. 'Program Counter' often intrigues students—what is it counting?
Explore the full memory hierarchy from registers (nanoseconds) to hard drives (milliseconds)—a factor of a million! Discuss why SSDs transformed gaming load times and why game developers carefully manage memory.
Connection: Deepens understanding of cache and registers by placing them in context of the full memory system. Explains real-world performance issues students experience.
Further Reading:
CPU cache is incredibly expensive to manufacture—that's why it's measured in MB while RAM is measured in GB. Discuss how Intel and AMD make different cache decisions and how this affects gaming performance.
Connection: Directly connects to cache understanding and previews performance factors (1.1.2) by showing cache size as a design decision with real trade-offs.
Support:
Stretch:
Tool showing relative speeds of different memory types
Prerequisites: 1
In 1945, one mathematician wrote a single paper that would define how almost every computer would work for the next 80 years. What did he figure out?
Show image of von Neumann. Ask: 'This man designed the basic architecture used in your phone, laptop, games console, and almost every computer on Earth. In 1945. Before computers as we know them existed.' Display his 'First Draft of a Report on the EDVAC'—a 101-page document that became the blueprint for modern computing. Key insight: STORE THE PROGRAM IN MEMORY—revolutionary because early computers were 'programmed' by physically rewiring them. Ask: 'Why would storing the program in memory be such a big deal?'
Resources:
Historical images to set context
Images of ENIAC programmers physically rewiring the machine
Teacher Notes:
The contrast between rewiring a computer and loading a program really lands. Ask students to imagine reprogramming their phone by opening it up with a screwdriver!
Core teaching video covering: (1) The stored program concept—instructions and data share the same memory, (2) The five key components: CPU, Memory, Input, Output, Bus, (3) Focus on the special registers: MAR (holds memory ADDRESS we want to access), MDR (holds DATA being read/written), Program Counter (holds address of NEXT instruction), Accumulator (holds calculation RESULTS), (4) Key distinction: Some registers hold ADDRESSES (where to look), others hold DATA (what we found).
Resources:
Animated explainer with clear register explanations
One-page summary: register name, purpose, holds address or data
Teacher Notes:
The address vs data distinction is crucial and often confusing. Use analogy: MAR is like a house number (address), MDR is like what's inside the house (data).
Enhanced Human CPU activity with specific register roles. Students wear labels: MAR, MDR, Program Counter, Accumulator, CU, ALU, Memory. Work through a simple program (e.g., ADD two numbers from memory). At each step, narrate which register is doing what. After physical activity, students complete a 'register trace table' showing the contents of each register at each step. Online version: Interactive step-through simulator with register highlighting.
Resources:
Printable badges for each register/component
Simple program to execute (LOAD, ADD, STORE)
Table for recording register contents at each step
Step-by-step CPU simulator with register visualization
Teacher Notes:
Go SLOWLY. Stop at each step and ask: 'What's in the MAR now? The MDR? Why?' Building this trace-through skill is essential for exam success.
Focused reading on the crucial distinction between addresses and data. Use post box analogy: An address tells you WHERE to look (like a postcode), data is WHAT you find there (like the letter inside). Practice questions: 'The Program Counter holds an... (address)', 'The Accumulator holds... (data)'. Apply to real scenario: When CPU needs to fetch instruction 42, what goes in MAR? (42—the address). What appears in MDR? (The instruction itself—the data).
Resources:
Illustrated document with postbox analogy
Self-assessment questions on address vs data
Teacher Notes:
This distinction is a common exam question. Ensure all students can confidently categorise each register.
Drag-and-drop activity where students arrange the steps of fetch-execute in order, then label which registers are involved at each step. Show animation of their arrangement to verify. Challenge version: Given a program, predict register contents after each cycle. Includes reflection: 'Why does this cycle need to repeat billions of times per second?'
Resources:
Interactive ordering activity
Predict-the-register-content exercises
Teacher Notes:
Common mistake: mixing up FETCH (get instruction from memory) with DECODE (understand what it means). Ensure these are clearly separated.
Quiz focusing on: What does MAR stand for? Does it hold an address or data? What's the Program Counter for? What would happen if the Program Counter stopped working? Branching feedback. Consolidation: Students create a mnemonic for remembering the four registers and what each does.
Resources:
Interactive quiz with register-focused questions
Template for creating memory aids
Teacher Notes:
The 'what if it broke' questions encourage deeper understanding. PC broken = computer doesn't know what to do next. MDR broken = can't read or write data.
Brief biography of von Neumann—a genuine polymath who contributed to quantum mechanics, game theory, nuclear weapons, economics, AND computer science. He could memorise entire books and do complex calculations in his head. Discuss how his architecture was revolutionary because it stored programs in memory alongside data.
Connection: Understanding the historical context helps students appreciate why this architecture was revolutionary and why it's still used today.
Further Reading:
Brief introduction to Harvard architecture (separate memory for instructions and data) used in microcontrollers. Discuss why different architectures suit different purposes—previews embedded systems discussion.
Connection: Understanding that Von Neumann is ONE architecture choice deepens appreciation of the design decisions. Links to embedded systems (1.1.3).
Discuss limitations of shared data/instruction bus and how this affects AI and modern computing. Introduce the concept that computer architecture is still evolving and there are unsolved problems.
Connection: Shows that CPU architecture is a living field with ongoing challenges—careers exist in solving these problems.
Support:
Stretch:
https://www.peterhigginson.co.uk/lmc/ - Visual Von Neumann simulator
https://web.archive.org/web/20130314123032/http://qss.stanford.edu/~godfrey/vonNeumann/vnedvac.pdf
Prerequisites: 1, 2
A £500 gaming PC can have a 'faster' CPU than a £2000 laptop. How can that be? And why do gamers argue endlessly about AMD vs Intel?
Display two CPU specs side by side: CPU A (4.5 GHz, 4 cores, 8MB cache) vs CPU B (3.2 GHz, 8 cores, 32MB cache). Ask: 'Which is faster?' Let students debate. Reveal: 'It depends on what you're doing!' Different tasks benefit from different specs. This lesson will teach you how to actually understand CPU specifications.
Resources:
Side-by-side spec comparison
Prompts for each position
Teacher Notes:
This deliberately has no clear answer. Gaming often favours high clock speed; video editing favours many cores. Build this tension before resolving it.
Core teaching video covering: (1) CLOCK SPEED (measured in GHz): How many cycles per second—like a drummer setting the beat, (2) CACHE SIZE (measured in MB): Bigger cache = more data instantly available—links to lesson 2, (3) NUMBER OF CORES: Each core is a separate processor—like having multiple workers. Include real-world examples: Why games want high clock speed (fast single tasks), why video rendering wants many cores (parallel tasks), why professional workstations have huge caches.
Resources:
Animated explainer with real benchmark footage
Reference document with key information
Teacher Notes:
Use the drummer analogy for clock speed—everyone works to the beat. For cores, use kitchen analogy: one chef vs five chefs.
Students work as 'CPU consultants'. Given different client briefs (gamer wanting high FPS, video editor rendering 4K, student doing homework, server handling thousands of requests), recommend CPU priorities and explain reasoning. Must consider budget constraints. Present recommendations to class. Online version: interactive scenario selector with feedback on choices.
Resources:
Descriptions of different users and their needs
Fictional CPUs with different spec combinations
Structure for presenting CPU advice
Interactive version for remote learners
Teacher Notes:
Encourage trade-off thinking: 'If you prioritise X, you might sacrifice Y.' Real-world CPU selection always involves compromises.
Detailed reading on: How clock speed is measured (cycles per second, Hz→MHz→GHz), why 'bigger number isn't always better' (architecture matters), how multiple cores work in parallel, when parallel processing helps and when it doesn't. Includes worked example calculating theoretical performance. Students answer comprehension questions.
Resources:
Illustrated technical explanation
Self-check questions on the reading
Teacher Notes:
The 'multiple cores can't help some tasks' point is important. Analogy: Two chefs can make two pizzas faster, but two chefs can't make one pizza twice as fast.
Interactive tool where students adjust sliders for clock speed, cache size, and core count (within a fixed 'budget'). See simulated performance across different tasks (gaming, video editing, web browsing, machine learning). Discover that there's no 'best' configuration—it depends on use case. Record observations: Which configuration worked best for which task? Why?
Resources:
Browser-based interactive tool
Template for recording findings
Teacher Notes:
This reinforces that CPU 'speed' is multidimensional. Students should discover that optimising for one task may hurt another.
Brief discussion on the environmental cost of faster CPUs: higher power consumption, more heat (data centres use massive cooling), short upgrade cycles creating e-waste. Show data on data centre energy usage. Ask: 'Do we need the fastest possible CPU, or is 'fast enough' more responsible?' Introduce concept of right-sizing technology.
Resources:
Infographic on tech industry energy use
Questions about responsible technology consumption
Teacher Notes:
This is a rare chance to discuss ethics in a technical unit. No need to moralise—just raise awareness that choices have consequences.
Quiz covering: What does GHz measure? How do more cores help? When would a bigger cache help most? Given specs, predict which tasks each CPU suits best. Branching feedback for misconceptions. Exit ticket: 'Write three questions you would ask before buying a CPU.'
Resources:
Interactive quiz with scenario-based questions
Three-question format
Teacher Notes:
The exit ticket questions reveal understanding. Good questions show they grasp that it depends on use case.
Discuss how CPU benchmarks work, why companies choose flattering benchmarks, and how to interpret real-world performance reviews. Introduce critical media literacy around tech marketing.
Connection: Applies understanding of performance factors to real-world decision-making and develops critical evaluation skills.
Further Reading:
Gordon Moore predicted in 1965 that transistor density would double every ~2 years. This held true for 50+ years, driving the exponential improvement in computers. Discuss whether Moore's Law is ending and what that means for the future.
Connection: Provides historical context for why CPUs keep getting faster and raises questions about future developments.
Further Reading:
Faster CPUs require more power and generate more heat. Discuss: energy consumption of data centres, e-waste from rapid upgrades, rare earth materials in chip manufacturing, and the ethical implications of the constant upgrade cycle.
Connection: Connects technical knowledge to broader social, economic, and environmental considerations, developing responsible digital citizenship.
Support:
Stretch:
Prerequisites: 1, 2
How many computers did you interact with before you even got to school today? The answer might surprise you...
Interactive opener: 'From waking up to arriving here, how many computers did you interact with?' Students brainstorm in pairs. Reveal likely candidates: alarm clock, smartphone, microwave, fridge, car/bus, traffic lights, automatic doors, payment terminal, security cameras... Show that many of these aren't 'computers' in the traditional sense—they're EMBEDDED SYSTEMS. Ask: 'What makes these different from your laptop?'
Resources:
Illustrated timeline showing embedded systems encountered
Prompts for brainstorming
Teacher Notes:
Students are often amazed at the number. Keep a running tally on the board. Some estimates suggest we interact with 50+ embedded systems daily.
Core teaching video covering: (1) Definition: A computer designed to do ONE specific task, built INTO a larger device, (2) Key characteristics: Dedicated purpose, often real-time, limited user interface, power-efficient, reliable, (3) Comparison with general-purpose computers: Your laptop can run any software; a washing machine's computer only runs washing machine code, (4) Examples across categories: Home (microwave, thermostat, TV remote), Transport (car engine management, train signals), Medical (pacemakers, insulin pumps), Industrial (factory robots, power grid sensors).
Resources:
Animated explainer with real-world footage
Side-by-side reference document
Teacher Notes:
Emphasise that embedded doesn't mean 'simple'—a car's embedded systems are incredibly sophisticated. But they're dedicated to one purpose.
Students investigate a specific embedded system in depth. Options: fitness tracker, smart thermostat, car parking sensor, gaming controller, electric toothbrush. For each, identify: What's its ONE main job? What inputs does it receive? What outputs does it produce? Why is an embedded system better than using a general PC? Create a mini-poster or digital presentation. Gallery walk to see others' investigations. Online version: Collaborative document with assigned devices.
Resources:
Structured analysis template
Background info on each device option
Printable or digital template
Teacher Notes:
Ensure coverage of different categories. Some students might want to investigate their own device—encourage this if time allows.
Focused reading on embedded system characteristics: Dedicated single function, Real-time operation (must respond immediately), Limited resources (small memory, low power), Reliability requirements (must work continuously without crashes), Limited/no user interface, Hard to modify once deployed. Students complete a checklist exercise: 'Is this an embedded system?' for various devices.
Resources:
Detailed explanation of each characteristic
Classification exercise with varied examples
Teacher Notes:
The 'hard to modify' point is interesting—contrast with how easily you update phone apps. Embedded systems are often 'set and forget'.
Discussion-based segment exploring ethical considerations. Case study 1: Smart home devices that listen constantly—privacy implications. Case study 2: Self-driving car must make split-second decisions—who programs the ethics? Case study 3: Medical devices—when software bugs can be fatal. Students discuss in groups, then share perspectives. No 'right answers'—goal is awareness.
Resources:
Three scenario cards with discussion questions
Structure for respectful ethical discussion
Teacher Notes:
These discussions can get lively. Establish ground rules for respectful disagreement. Emphasise that these are real questions engineers face.
Final quiz covering all embedded systems content: Definition, characteristics, examples. Also include mixed review questions from entire unit (CPU purpose, registers, performance factors) to consolidate learning. Branching feedback for wrong answers. Unit reflection: 'What surprised you most about how computers work? What do you want to learn more about?'
Resources:
Quiz covering embedded systems and unit review
Structured reflection prompts
Teacher Notes:
The reflection helps identify topics for revision and gauges whether we've achieved the 'inspire' goal. Look for genuine curiosity in responses.
Explore how embedded systems are connecting to create the 'Internet of Things'—smart homes, connected cars, industrial sensors. Discuss opportunities and risks (privacy, security, job changes).
Connection: Extends embedded systems understanding to show where the field is heading and raises awareness of career opportunities.
Further Reading:
Case studies of embedded system failures: Boeing 737 MAX, Toyota unintended acceleration, medical device recalls. Discuss the ethics of software quality in life-critical systems and why testing embedded systems is challenging.
Connection: Introduces real-world stakes of embedded system design, highlighting career responsibility and ethical considerations.
Overview of embedded systems careers: automotive software engineer, medical device developer, IoT developer, robotics engineer. Show salary ranges and required skills. Highlight that this is a growing field with strong UK presence (automotive, aerospace, medical).
Connection: Directly connects specification content to career pathways, supporting course goal of inspiring career interest.
Support:
Stretch:
Prerequisites: 1