Embedded systems: hardware and software

What an embedded system is

An embedded system is a computer system with a dedicated function inside a larger mechanical or electrical system. It usually has to be small, cheap, low power and reliable, often runs in real time and may run for years without a restart. Examples: engine management unit, smart thermostat, pacemaker, washing machine controller.

Hardware components

• Microprocessor or, more often, a microcontroller unit (MCU): a single chip holding a processor core, memory and I/O ports.
• Memory: flash/ROM for the program, RAM for working data.
• I/O ports and interfaces: connect sensors, actuators, displays and networks.
• Sensors: measure the physical world, for example accelerometer (movement and tilt), vibration, sound (microphone), temperature.
• Actuators: receive electrical control signals and turn them into physical action: motors, valves, relays, heaters, buzzers.
• Power supply: battery or mains, often with power-saving modes.
• ADC and DAC: an analogue-to-digital converter turns sensor voltages into numbers; a digital-to-analogue converter turns numbers back into voltages (next lesson).

Software components

• Firmware: software stored in non-volatile memory that controls the hardware directly; updated rarely ('flashing').
• Operating system: often none (a single control loop) or a small real-time operating system that guarantees response times.
• Application software: the code for the device's task, for example the thermostat's control logic.
• Languages: C and C++ are common because they give close control of memory and hardware; assembly for time-critical parts; MicroPython on some boards.

Benefits and drawbacks

Benefits: cheap to mass produce, small, low power, reliable, fast dedicated response, easy for the user.

Drawbacks: limited processing power and memory; hard or impossible to upgrade; difficult to debug; connected devices can be hard to patch, which creates security risks.

A design diagram usually reads: sensor -> ADC -> microcontroller (firmware and application) -> DAC or driver -> actuator, with a power supply feeding everything.

Worked example

Describe how a smart thermostat keeps a room at 21 °C.

1. A temperature sensor produces a voltage; the ADC converts it to a number.
2. The microcontroller's software compares the reading with the set point of 21 °C.
3. If the room is too cold, it sends a signal through an output port to an actuator (a relay) that switches the boiler on; when 21 °C is reached, it switches it off.
4. This loop repeats continuously.

Answer: Sensor, ADC, compare with set point in the MCU, actuator output, repeat.

Check yourself

1. What is an embedded system?
   • A general-purpose desktop computer
   • A program stored in the cloud
   • A virtual machine on a server
   • A computer with a dedicated function inside a larger device
   Show answer

   A computer with a dedicated function inside a larger device. It is built in, dedicated and usually invisible to the user.

2. What does a microcontroller unit (MCU) contain on a single chip?
   • Only an ALU
   • A processor core, memory and input/output ports
   • A hard disk and a graphics card
   • A keyboard controller and a monitor
   Show answer

   A processor core, memory and input/output ports. That integration is why MCUs suit cheap, small embedded devices.

3. How does an actuator work?
   • It converts physical quantities into electrical signals
   • It stores the firmware
   • It converts analogue signals to digital
   • It receives electrical control signals and converts them into physical movement or action
   Show answer

   It receives electrical control signals and converts them into physical movement or action. Actuators are outputs: motors, valves, relays.

4. Which sensor would a fitness band use to count steps?
   • Accelerometer
   • Temperature sensor
   • Microphone
   • Light-dependent resistor
   Show answer

   Accelerometer. An accelerometer measures acceleration and changes in movement.

5. What is firmware?
   • The plastic case around the circuit board
   • A cloud service used by the device
   • Software stored in non-volatile memory that directly controls the device's hardware
   • Temporary data in RAM
   Show answer

   Software stored in non-volatile memory that directly controls the device's hardware. Firmware is held in flash or ROM and runs when the device starts.

6. Why is C commonly used for embedded software?
   • It gives close control over memory and hardware with small, fast code
   • It needs a large operating system to run
   • It is only used for web pages
   • It cannot access hardware ports
   Show answer

   It gives close control over memory and hardware with small, fast code. Limited memory and timing needs favour compact compiled code.

7. Which is a drawback of embedded systems?
   • They are always more expensive than PCs
   • They use more power than a desktop
   • They are often hard to update, so security flaws may stay unpatched
   • They cannot use sensors
   Show answer

   They are often hard to update, so security flaws may stay unpatched. Limited interfaces and resources make updates difficult.

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Sources

• Pearson Edexcel International Advanced Subsidiary and Advanced Level in Computer Science specification (2026), Issue 1
• Pearson Edexcel IAL Computer Science sample assessment materials (Unit 3 paper, resource booklet and mark scheme)

Last updated 8 November 2026. Spotted a mistake? Tell us.