Embedded Systems

This lesson covers embedded systems — a type of computer system built into a larger device to perform a specific, dedicated function. Embedded systems are examined in AQA and OCR GCSE Computer Science.

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What Is an Embedded System?

An embedded system is a computer system built into a larger device that is dedicated to performing one specific function (or a small number of related functions). Unlike a general-purpose computer (such as a laptop or desktop), an embedded system is designed to do one job and do it well.

Key Characteristics

Characteristic	Description
Dedicated function	Designed to do one specific task
Built into a larger device	Not a standalone computer
Limited or no user interface	May have simple buttons/LEDs rather than a screen and keyboard
Cannot be reprogrammed by the user	Software is usually fixed at manufacture (stored in ROM or flash memory)
Low power consumption	Often designed to run on batteries or small power supplies
Small and compact	Uses a small processor, limited memory, and few peripherals
Real-time operation	Often needs to respond instantly to inputs (e.g., a car airbag)

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Examples of Embedded Systems

Embedded systems are found in a huge range of everyday devices:

Device	Embedded System Function
Washing machine	Controls the wash cycle — temperature, spin speed, timer
Microwave oven	Controls cooking time, power level, and turntable motor
Traffic lights	Controls the sequence and timing of red, amber, and green lights
Central heating thermostat	Monitors temperature and switches heating on/off
Car engine management system	Monitors and controls fuel injection, ignition timing, emissions
Digital watch	Keeps time, controls display, manages alarms
TV remote control	Sends infrared signals corresponding to button presses
Fitness tracker	Monitors heart rate, counts steps, tracks sleep
Smart doorbell	Detects motion, captures video, sends notifications
Anti-lock braking system (ABS)	Prevents wheels from locking during braking

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How Do Embedded Systems Differ from General-Purpose Systems?

Feature	Embedded System	General-Purpose System
Purpose	Single, dedicated task	Many different tasks
User interface	Simple or none (buttons, LEDs)	Full (screen, keyboard, mouse)
Operating system	Often no OS, or a minimal real-time OS	Full OS (Windows, macOS, Linux)
Software	Fixed — cannot install new programs	Flexible — users install/remove software
Processing power	Low (only needs to handle one task)	High (handles multiple complex tasks)
Memory	Very limited	Large (GBs of RAM, TBs of storage)
Cost	Low (mass-produced, simple hardware)	Higher
Power consumption	Low	Higher
Examples	Washing machine, traffic lights, digital watch	Laptop, desktop, smartphone

Exam Tip: A common question is "Give two differences between an embedded system and a general-purpose system." Always include: (1) embedded systems are dedicated to one task while general-purpose systems can run many programs, and (2) embedded systems typically have no user-modifiable software while general-purpose systems allow users to install software.

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Components of an Embedded System

An embedded system typically contains:

1. Processor (microcontroller) — a small, low-power CPU that runs the embedded program.
2. ROM or flash memory — stores the program permanently (non-volatile).
3. Small amount of RAM — for temporary data during operation.
4. Input sensors — detect conditions in the real world (e.g., temperature sensor, motion sensor, button press).
5. Output actuators — perform actions in the real world (e.g., motor, heater, LED, buzzer).

+--------------------------------------------------+
|              Embedded System                      |
|                                                   |
|  [Sensors] --> [Microcontroller] --> [Actuators]  |
|                  (Processor +                     |
|                   ROM + RAM)                      |
+--------------------------------------------------+

Microcontroller vs Microprocessor

Feature	Microcontroller	Microprocessor
Contains	CPU + memory + I/O on one chip	CPU only (needs external memory and I/O)
Used in	Embedded systems	General-purpose computers
Cost	Very low	Higher
Power	Very low	Higher
Example	Arduino, PIC	Intel Core, AMD Ryzen

Embedded vs General-Purpose at a Glance

graph TD
    A["Computer System"] --> B["Embedded System"]
    A --> C["General-Purpose System"]
    B --> D["Dedicated function"]
    B --> E["Microcontroller (CPU + RAM + flash)"]
    B --> F["Sensors and actuators"]
    B --> G["Fixed firmware in ROM"]
    C --> H["Many tasks"]
    C --> I["Microprocessor + RAM + storage"]
    C --> J["Full operating system"]
    C --> K["User-installable software"]

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Advantages of Embedded Systems

• Cheap to produce — simple hardware, mass-manufactured.
• Reliable — designed for one task, so fewer things can go wrong.
• Low power consumption — can run on batteries for extended periods.
• Small and lightweight — can fit inside compact devices.
• Fast response — optimised for their specific task, often operating in real-time.

Disadvantages of Embedded Systems

• Cannot be easily reprogrammed — if a bug is found, the device may need replacing or a firmware update.
• Limited functionality — can only do what they were designed for.
• Difficult to upgrade — hardware and software are tightly integrated.
• Limited user interface — may be difficult for users to interact with.

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Real-World Example: A Washing Machine

A washing machine contains an embedded system that:

1. Reads inputs: water temperature sensor, door lock sensor, user-selected program (buttons/dial).
2. Processes: the microcontroller runs a fixed program stored in ROM that determines the wash cycle sequence.
3. Controls outputs: water valve (fill), heater (temperature), motor (spin), drain pump (empty), display (timer/status).

The user selects a program and presses start. The embedded system then runs the entire wash cycle automatically without any further user input.

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Summary