Embedded systems
OCR J277 Paper 1 frequently sets 2–4 mark questions on embedded systems — usually asking for a definition, characteristics, or examples. The exam expects students to distinguish embedded systems from general-purpose computers.
📖Definition
An embedded system is a computer system built into a larger device to perform a specific, dedicated function. Unlike a desktop PC, the user does not install or change the software during normal use.
Key characteristics
- Dedicated purpose — designed for one task (e.g. controlling a washing-machine cycle).
- Built into hardware — the CPU, memory and software are integrated with the device.
- Limited resources — small CPU, small RAM, limited storage compared with a PC.
- Often real-time — must respond to inputs within strict time limits.
- Software stored in ROM/flash — typically not changed by the end user; some products allow firmware updates.
- Low power consumption — many run on batteries or small power supplies.
- Reliable and stable — fewer features means fewer faults; designed to run continuously for years.
✦Worked example— Examples
| Device | Function the embedded system controls |
|---|---|
| Washing machine | Drum speed, water valves, cycle timing |
| Microwave oven | Power level, timer, door interlock |
| Vehicle ECU (Engine Control Unit) | Fuel mixture, ignition timing, sensor monitoring |
| Smart thermostat | Temperature reading, heating control, scheduling |
| Digital camera | Sensor read-out, autofocus, image processing |
| Traffic-light controller | Light sequencing, sensor input from road loops |
Embedded vs general-purpose computer
| Feature | Embedded | General-purpose (PC) |
|---|---|---|
| Purpose | Single, dedicated | Many uses |
| User installs software? | No (firmware fixed) | Yes |
| Resources | Limited | Large |
| Operating system | Often a small RTOS or none | Full OS (Windows, macOS, Linux) |
| Cost | Low per unit | Higher |
Common OCR exam mistakes
- Calling a smartphone an embedded system — it is general-purpose because the user installs apps.
- Forgetting that embedded systems are inside a larger device.
- Listing only examples without giving the function the embedded system performs.
AI-generated · claude-opus-4-7 · v3-ocr-computer-science-leaves