Understand input devices and their purposes

Input and Output Devices – IGCSE 0478

Learning Objectives

• Define input and output devices and explain why they are required.
• Identify a wide range of common input devices, the type of data they capture and typical uses.
• Distinguish between primary and secondary input devices.
• Explain the basic operation of input devices (transduction, ADC, drivers, interfaces).
• Recognise sensors as specialised input devices and give examples.
• Identify common output devices, the form of data they present and typical uses.

What Is an Input Device?

An input device is any hardware that allows a user or the environment to send data, commands or instructions to a computer. It converts a physical action, an analog signal or a sensed phenomenon into digital information that the CPU can process.

Categories of Input Devices

• Manual input devices – operated directly by the user (e.g., keyboard, mouse).
• Automatic input devices – capture data without continuous user manipulation (e.g., scanner, microphone).
• Special‑purpose input devices – designed for particular tasks such as gaming, graphics or accessibility.
• Sensors – detect physical quantities (light, temperature, motion, proximity, etc.) and output an electrical signal that is then digitised.

Common Input Devices – Purpose, Data Captured & Typical Use

How Input Devices Work – Basic Process

1. Physical action or sensed phenomenon occurs (e.g., a key press, light hitting a sensor).
2. Transduction: The device hardware converts the action into an analogue electrical signal.
3. Analog‑to‑Digital Conversion (ADC): The signal is sampled at a specific sampling rate and quantised to a set resolution (e.g., 8‑bit, 16‑bit).
4. Device Driver interprets the raw binary data and presents a standardised interface to the operating system.
5. Interface / Transmission: Data is sent to the computer via USB, Bluetooth, PS/2, HDMI, Wi‑Fi, etc.
6. Operating System receives the data, stores it in an input buffer, and makes it available to applications.
7. Application reads the data and acts on it (e.g., displays a character, moves a cursor).

Key technical terms to remember:

• Sampling rate – how often the analogue signal is measured (samples per second).
• Resolution – the number of distinct values each sample can represent (bit depth).
• Latency – the delay between the physical action and the computer’s response.
• Driver – software that translates hardware signals into a form the OS understands.

Primary vs. Secondary Input Devices

• Primary input devices – essential for everyday interaction with a computer (e.g., keyboard, mouse, touchscreen).
• Secondary input devices – provide additional or specialised functionality (e.g., scanner, microphone, barcode reader, sensors).

Note: The Cambridge syllabus does not require the terms “primary” and “secondary”, but the distinction helps students organise revision.

Sensors – Specialized Input Devices

Sensors detect changes in the physical world and output an electrical signal that is then digitised. They are widely used in embedded systems, robotics, mobile devices and the Internet of Things (IoT).

• Accelerometer – measures linear acceleration.
• Gyroscope – measures angular rotation.
• Light / Colour sensor – measures ambient light intensity or colour.
• Temperature sensor – measures heat.
• Proximity sensor – detects the presence of nearby objects.

What Is an Output Device?

An output device converts digital data from the computer into a form that can be perceived by the user or the environment (visual, auditory, tactile or physical).

Common Output Devices – Purpose, Data Presented & Typical Use

Suggested Diagram

Key Points to Remember

• All input devices ultimately produce digital data that the CPU can process.
• Output devices translate digital data into a form perceivable by humans or other systems.
• Device categories (manual, automatic, special‑purpose, sensor) help organise study and revision.
• Primary input devices are required for everyday use; secondary devices extend functionality.
• Drivers and interface standards (USB, Bluetooth, PS/2, HDMI, Wi‑Fi) are essential for communication between hardware and software.
• Sampling rate, resolution and latency affect the quality and responsiveness of input devices.

Practice Questions

1. Match each device to the type of data it captures (audio, image, text, motion, temperature, proximity, etc.).
2. Explain why a scanner is classified as an automatic input device rather than a manual one.
3. Identify two situations where a special‑purpose input device would be preferable to a standard keyboard and mouse, and justify your choice.
4. Describe the role of a device driver in the operation of an input device.
5. List three output devices and state the form of data each presents to the user.
6. Give an example of a sensor used in everyday technology and explain the physical quantity it measures.