Syllabus & Goals 3 min
Cambridge 3.1 · Computer architecture Paper 1 · Computer Systems
By the end of this lesson you can:
- Explain how clock speed, cores and cache affect CPU performance.
- State the risks of overclocking.
- Describe what an embedded system is, with examples and trade-offs.
Recap / Warm-Up 5 min
You know what a CPU contains. Now: what makes one CPU faster than another — and where do tiny CPUs live in everyday devices?
Quick starter
A CPU runs at 3.5 GHz. Roughly how many clock cycles is that per second?
Reveal the answer
3.5 billion cycles per second (1 GHz = 1 000 000 000 cycles/second). Each cycle the CPU can do a small step of work.
Key Concept 14 min
1 · What affects CPU performance
- Clock speed — the number of cycles per second (GHz). Higher usually means faster.
- Number of cores — each core is its own CU + ALU + registers. Dual-core / quad-core CPUs can run tasks in parallel.
- Cache size — cache is fast memory inside the CPU that stores frequently used data/instructions, so the CPU avoids the slower RAM.
- Bus width — wider address/data buses move more at once.
Overclocking means running the clock faster than designed. It can speed things up, but risks overheating and instability / crashes as instructions fail to finish in time.
2 · Embedded systems
They are built around a microcontroller (a CPU plus some RAM/ROM and I/O on one chip), a microprocessor, or a system-on-chip. You find them in cars (ABS, airbags, engine management), washing machines, vending machines and security alarms.
Worked Example 12 min
(a) Improving performance — and the catch
| Change | Effect | Catch |
|---|---|---|
| Raise clock speed | More cycles/second | More heat; overclocking can crash the CPU |
| Add more cores | Run tasks in parallel | Cores must communicate; software may not use them |
| Increase cache | Fewer slow RAM trips | Cache is expensive; limited size |
(b) An embedded system: a vending machine
- Inputs: keypad selection, coin/temperature/tilt sensors.
- Process: a microcontroller checks the money and the selection.
- Outputs: actuators turn the motor to dispense the item; an LCD shows the change; sales data is sent back to the operator.
Try It Yourself 12 min
Goal: Give two factors that affect how fast a CPU runs.
Goal: A washing machine uses an embedded system. Describe one input, the process and one output.
Goal: Explain why a desktop PC is not classed as an embedded system.
📝 Exam Practice 10 min
Define the term embedded system.
Mark scheme
- Hardware and software built into a device to perform a specific task (1).
Explain how increasing cache size can improve CPU performance.
Mark scheme
- Cache stores frequently used data/instructions inside the CPU (1)…
- …so the CPU accesses the slower RAM less often (1).
Give two risks of overclocking a CPU.
Mark scheme
- Any two of: overheating · instability / crashing · unreliable / unsynchronised operation (1 each, max 2).
Recap & Key Terms 3 min
CPU performance depends on clock speed, cores, cache and bus width; overclocking risks heat and crashes. An embedded system is hardware + software dedicated to one task, built around a microcontroller.
- Clock speed
- Cycles per second (GHz) — how fast the CPU steps through work.
- Core
- A complete processing unit (CU + ALU + registers); multi-core CPUs work in parallel.
- Cache
- Fast memory inside the CPU holding frequently used data/instructions.
- Embedded system
- Hardware and software built into a device to do one specific job.
Homework 1 min
Task (≤ 15 min): List three devices in your home that contain embedded systems, and for each state the one task it is dedicated to.
Model answer (examples)
- Microwave oven — controlling cooking time and power.
- Washing machine — running the chosen wash cycle.
- Air-conditioner — keeping the room at a set temperature.