What embedded systems are
An embedded system is a computer built into a larger device to perform one specific task, or a small set of tasks.
The contrast that makes the definition useful is with a general purpose computer. A laptop can run any program you install on it. A washing machine's controller runs one program, permanently, and cannot be made to do anything else — and that is a deliberate design choice, not a limitation.
Typical characteristics of an embedded system, which is what the specification asks for:
• Built into a larger device rather than being a computer in its own right • Performs a single dedicated function • Its program is stored permanently and is rarely, if ever, changed by the user • Small physical size and low power consumption • Cheap to produce in quantity • Very reliable, and usually needs no maintenance • Often has no conventional keyboard or screen — the controls are the device's own buttons and display
- Embedded system
- a computer built into a larger device to perform one specific task, or a small set of tasks, unlike a general purpose computer which can run any program installed on it
Examples
The specification asks for familiarity with a range of different embedded systems, so it is worth having examples from several settings rather than several washing machines:
• Household — washing machines, microwaves, dishwashers, central heating thermostats • Vehicles — engine management, anti-lock braking, parking sensors • Entertainment — digital cameras, televisions, MP3 players • Medical — pacemakers, blood pressure monitors • Public and industrial — traffic lights, vending machines, ticket machines, factory robots
A good test when you are unsure: could the user install a different program on it? If not, and it is built into something larger, it is an embedded system.
Worked example
Explain why a manufacturer would use an embedded system rather than a general purpose computer to control a microwave oven.
- Identify what the task actually needs: timing, power level and a display — a very narrow set of functions.
- A general purpose computer would provide far more than that, at greater cost.
- Cost matters in a product sold in quantity, so a cheaper dedicated controller is a real saving on every unit.
- Size and power: the controller must fit inside the appliance and draw little power.
- Reliability: fixed software that never changes means far less to go wrong, and the microwave needs no updates or maintenance.
Answer: The task needs only timing, power control and a display, so a general purpose computer would be unnecessarily expensive, large and power-hungry. A dedicated embedded controller is cheap enough to include in every unit, small enough to fit inside, and — because its program is fixed and does one job — far more reliable and maintenance-free.
Common mistake
A smartphone is not an embedded system, even though it is small and portable. Users install and remove software on it, so it is general purpose — though it contains embedded systems within it, such as the camera controller.
Before you practise
- An embedded system is a computer built into a larger device to perform one specific task.
- Its program is stored permanently and is not changed by the user.
- Characteristics: small, low power, cheap, reliable, dedicated to one function, often with no keyboard or screen.
- General purpose computers run any software the user installs; embedded systems do not.
- Examples span household appliances, vehicles, entertainment, medical devices and public machinery.
- A smartphone is general purpose, but contains embedded systems inside it.