A computer is useless if it cannot take in data or show what it has done. Input devices turn the real world into data; output devices turn data back into something people can see, hear or hold.
An input device allows data to be entered into a computer so that it can be processed; it is needed because the computer cannot process data it does not have. An output device takes the results of processing and presents them in a form people (or other devices) can use: on a screen, on paper, as sound or as movement. Input devices capture data; output devices display, produce or act on it.
Each input device converts something from the real world (a key press, light, sound, a pattern) into binary data the computer can process.
| Device | How it captures data | Example use |
|---|---|---|
| Keyboard | Each key press closes a circuit; the key is identified and its character code sent | Typing text |
| Optical mouse | An LED lights the surface; a small camera takes many images per second and changes between them show the movement | Moving a pointer |
| Microphone | Sound waves vibrate a diaphragm, producing an analogue electrical signal that an ADC converts to digital | Voice recording, video calls |
| Digital camera | Light passes through a lens onto a sensor made of millions of light-sensitive pixels; each is stored as a binary colour value | Photographs, video |
| Barcode scanner | Shines light on the black and white bars; dark bars reflect little light and light bars reflect more; the pattern is converted to a number | Shop checkouts, library books |
| QR code scanner | A camera captures the 2D pattern of black and white squares; software decodes it (it can hold far more data than a barcode) | Opening a website, tickets, payments |
Say why a device is an input device: it sends data into the computer for processing. A touch screen is both an input and an output device.
The syllabus names three kinds of touch screen. Each detects the position of a touch in a different way, which decides where it is best used.
| Type | How it works | Points to note |
|---|---|---|
| Resistive | Two flexible conductive layers separated by a gap; pressing pushes them together and the point of contact is calculated | Works with a gloved finger or stylus; cheap; less clear, can be scratched; needs pressure |
| Capacitive | The glass holds an electrostatic field; a finger (which conducts) changes the charge at that point and sensors locate it | Clear, durable, multi-touch; does not work with ordinary gloves |
| Infra-red | A grid of infra-red beams across the screen; a touch breaks beams and the sensors find which ones | Works with any object; good for large screens; affected by strong light or dirt |
Four quick checks. Each correct answer earns XP and records this skill on your profile.
Why does a computer need input devices?
Which touch screen detects a touch from a finger changing an electrostatic field?
Which device is an output device?
How does a DLP projector form an image?
Output devices present the results of processing. Learn one key fact about how each works and one typical use.
| Device | How it works | Example use |
|---|---|---|
| LCD screen | Liquid crystals in each pixel block or let through light from a backlight (usually LEDs) | Monitors, TVs |
| LED screen | Each pixel is made of tiny light emitting diodes (red, green and blue) that give out their own light | Large outdoor displays |
| DLP projector | Millions of tiny mirrors tilt to reflect light towards or away from the screen | Classrooms, cinemas |
| LCD projector | Bright light passes through LCD panels that form the image, then through a lens | Presentations |
| Inkjet printer | Tiny droplets of ink are sprayed onto paper through nozzles in a moving print head | Home photo printing, low volume |
| Laser printer | A laser builds a pattern of charge on a rotating drum; toner sticks to it, is transferred to paper and fused by heat | Offices, large volumes, fast |
| 3D printer | Builds a solid object layer by layer from a digital design (additive manufacturing) | Prototypes, prosthetics |
| Speaker | A digital signal is converted to analogue (DAC); the current moves a coil and cone that vibrate the air | Music, alerts |
| Actuator | A motor, valve or switch that causes physical movement in response to a signal | Opening a window in a greenhouse |
An actuator is an output device: it receives a signal from the processor and makes something move.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 1 standard.
Which printer uses a rotating drum, toner and heat?
Which input device would be best for capturing a solid object to make a digital model?
Why can a QR code hold more data than a barcode?
Which touch screen works with any object, using beams that are broken by a touch?
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