An embedded system is a computer built into a larger device to carry out one dedicated function. A general-purpose computer such as a laptop can run many different programs. A “discuss” question about an embedded system expects you to give a point, explain it, and link it to the device in the question.
This lesson draws on hardware and processing and on the software roles in operating system and application roles.
What makes a system embedded?
- It has one fixed job, or a small set of related jobs.
- Its program is stored permanently in memory inside the device, and users do not install new programs.
- It has a simple user interface: buttons, a small display or none at all.
- It is built into a machine, such as a rice cooker, a car or a security alarm.
What constraints does it work under?
| Constraint | What it means | Effect on the design |
|---|---|---|
| Cost | The product must be cheap to make | Simple processor, small memory |
| Size | The circuit must fit inside the device | Compact hardware |
| Power | Some run on batteries or must use little electricity | Efficient processor and program |
| Memory | Usually small | The program must be short and efficient |
| Timing | Some must respond within a fixed time | Fast, predictable responses |
| Upgrading | The program is stored in the device | Updates are difficult or impossible |
Worked example: a rice cooker
Discuss why a rice cooker is controlled by an embedded system rather than a general-purpose computer.
Step 1, state the job. The rice cooker has one dedicated function: read the temperature sensor, switch the heater on or off, and signal when the rice is done.
Step 2, link to constraints.
- Cost: a rice cooker is a low-priced appliance, so a small cheap processor is enough, while a full computer would make it too expensive.
- Memory: the program is short and fixed, so only a little memory is needed.
- Power and size: it uses little electricity and the circuit fits beside the heating plate.
Step 3, give the trade-off. The advantage is that the device is cheap, reliable and starts at once. The disadvantage is that it cannot run other programs and the program is hard to update. If the cooker later needs a new cooking mode, the manufacturer would probably have to build a new model.
Step 4, conclude in one sentence. A dedicated embedded system is the sensible choice because the job is fixed, the budget is small and no extra programs are needed.
The mistake to watch for
Mistaken answer: “An embedded system is a small computer such as a phone.”
A smartphone is a general-purpose computer, because users install many apps. An embedded system is defined by its dedicated job inside a larger device, not by its size.
A second common slip is listing constraints without applying them. “Limited memory” earns less than “limited memory, so the rice cooker’s program must be short and can only do cooking control”.
Check yourself
1. State two differences between an embedded system and a general-purpose computer.
Show answer
An embedded system does one dedicated task, while a general-purpose computer runs many programs. An embedded system’s program is stored permanently and rarely changed, while a general-purpose computer lets users install new software.
2. A traffic light controller is an embedded system. Give one constraint and explain it for this device.
Show answer
Timing: the lights must change at the right moments every cycle without delay, because a late change could cause an accident. So the controller needs a reliable, predictable response.
3. Give one advantage and one disadvantage of using an embedded system in a washing machine.
Show answer
Advantage: it is cheap and reliable because it only has to run washing programs. Disadvantage: it cannot run other software and is hard to update, so a new wash feature may need new hardware.
Where this leads next
You have now covered each part of the module. Try the software and systems practice set, and use the mistake log and retest queue to track wrong answers.
If you want help turning short facts into discussion paragraphs, that is something our teachers practise in online one-to-one Computer Science tuition.