Hardware components and how they work together

A computer system is a team: input devices, the CPU, main memory, secondary storage and output devices. Each has a clear job, and data flows between them.

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The main components

ComponentJobExamples
Input devicesCapture data and send it into the computerKeyboard, mouse, touchscreen, microphone, camera, scanner, barcode reader, sensors (such as temperature or light)
CPUFetches, decodes and executes instructions; processes the dataThe processor in a laptop or phone
Main memory (RAM)Holds the programs and data in use, so the CPU can reach them quickly8 GB of RAM
Secondary storageKeeps programs and files when the power is offHard disk, SSD, memory card, optical disc
Output devicesPresent the results to people or control thingsMonitor, printer, speakers, headphones, actuators such as motors and lights

How they work together

1. An input device turns something in the real world (a key press, a sound, a temperature) into binary data.
2. The data goes into RAM. The program that processes it has already been loaded from secondary storage into RAM.
3. The CPU fetches each instruction and the data from RAM, processes it and writes results back to RAM.
4. Results go to an output device, and can be saved to secondary storage for later.
This is the input, process, output model, with storage keeping data between uses.

Sensors and actuators

In control systems, such as a greenhouse or a central heating system, sensors are input devices that measure the environment, and actuators are output devices that make something happen, such as opening a window or switching on a heater.
The processor compares the sensor readings with stored values and decides what the actuators should do, again and again.
Worked example

A supermarket self-checkout scans a barcode and shows the price on a screen. Describe how the components work together.

  1. The barcode scanner (input) reads the barcode and sends its number as binary data.
  2. The CPU runs the checkout program held in RAM and looks up the product's price.
  3. The screen (output) shows the name and price; the sale is saved to storage.

Answer: Input: scanner. Process: CPU and RAM look up the price. Output: screen. Storage: the sale is recorded.

Key idea

Input devices capture data, the CPU processes it using programs and data held in RAM, output devices present the results, and secondary storage keeps everything when the power is off. Sensors are inputs; actuators are outputs.

Key words
Secondary storage
Non-volatile storage for files and programs: magnetic, optical or solid state.
RAM
Volatile main memory holding the programs and data in use.
Binary
Base 2: the number system that uses only the digits 0 and 1.

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Extra practice

2 more questions

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  1. In a car park barrier system, which is an input device?

    1. The motor that lifts the barrier
    2. The display screen
    3. A sensor that detects a car
    4. The ticket printer
    Show the answer

    Answer: A sensor that detects a car

    Sensors send data in.

  2. In an automatic greenhouse, which is an input device?

    1. Motor that opens a window
    2. Heater
    3. Sprinkler
    4. Temperature sensor
    Show the answer

    Answer: Temperature sensor

    Sensors are inputs.

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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