Input and Output Devices

An input device sends data into the computer for processing. Cambridge expects you to know all of these:

• Keyboard — typing, command input, navigation. Universal but slow for non-text input.
• Mouse / trackpad — pointing, selecting. Suited to graphical interfaces.
• Microphone — captures sound (speech, voice commands, recordings).
• Digital camera / webcam — captures still images and video.
• Scanner (flatbed, document, 3D) — converts physical originals into digital images.
• Barcode reader — reads 1D black-and-white bar patterns. Used in retail, libraries, warehouse picking.
• QR code reader — reads 2D matrix patterns. Holds far more data than a barcode (URLs, contact info).
• OCR / OMR — optical CHARACTER recognition (turns scanned text into editable text); optical MARK recognition (reads pencil marks on multiple-choice forms).
• Touch screen — input AND output in one (see touch-screen section).
• Sensors — capture real-world quantities (covered separately).

Cambridge tip. When a question asks for 'an input device', name a SPECIFIC device with a CLEAR PURPOSE — not 'a sensor' or 'a button'.

An output device receives data from the computer and presents it to the user or environment.

Visual outputs.

• Monitors — LCD, LED-backlit LCD, OLED. Higher PPI = sharper image.
• Projectors — fire light onto a surface for large-scale viewing.
• Touch screens as displays (input + output).

Print outputs.

• Inkjet printer — sprays liquid ink through nozzles. Cheap, photo-quality, slow, ink dries.
• Laser printer — fuses dry toner to paper using a heated drum. Fast, sharp, high-volume; higher upfront cost.
• 3D printer — additive manufacturing (full section below).

Audio outputs.

• Speakers / headphones — convert digital audio to sound waves via a digital-to-analogue converter (DAC).

Actuators. In process-control systems, the 'output device' is often an actuator that performs a PHYSICAL action — motors, valves, heaters, pumps, hydraulic rams. Specify which.

Cambridge tip. Mark schemes distinguish OUTPUT (information to a user — text, sound, image) from ACTUATOR (an action in the physical world). Use the right term for the context.

Three different touch-screen technologies appear in 0478 questions.

Resistive. Two flexible conductive layers separated by a tiny gap. When you press, the layers touch and complete a circuit at that point — coordinates derived from voltage drop.

• Pros: Works with any object (gloved finger, stylus). Cheap to manufacture.
• Cons: Less responsive — needs firm pressure. Layers wear out. Doesn't support multi-touch well.

Capacitive. A glass surface coated with a transparent conductor stores a small electric charge. A bare fingertip is conductive; touching changes the local charge field, which sensors at the corners detect.

• Pros: Very clear image; supports multi-touch (pinch, swipe, rotate); durable.
• Cons: Only works with conductive objects (skin, special styluses). Doesn't work through gloves.

Infrared. A grid of infrared LEDs projects beams across the screen surface; receivers detect when an object (any object) breaks the beams.

• Pros: Very durable (no surface layer to wear). Works with anything (gloves, stylus, finger). Can be made very large.
• Cons: Expensive. Affected by direct sunlight, dirt or water on the bezel.

Where each is used. Resistive: industrial control, payment terminals where styluses are used. Capacitive: smartphones, tablets, modern laptops. Infrared: large interactive whiteboards, digital signage, ATMs.

A 3D printer builds a physical object from a digital design using additive manufacturing — adding material layer by layer rather than removing it (like CNC machining).

The process:

1. CAD model. A 3D model is created using computer-aided design software, exported as a standard file (e.g. .stl).
2. Slicing. Slicer software divides the model into thin horizontal layers (each a 2D cross-section the printer can build).
3. Printing. The printer extrudes material (commonly thermoplastic filament — PLA, ABS — but also resin, metal powder, even concrete) along the X-Y plane while the bed lowers (or the head rises) one layer at a time.
4. Bonding. Each new layer fuses to the one below as it cools, building a solid 3D shape.
5. Post-processing. Supports may be removed; surfaces sanded; resin parts UV-cured.

Real-world uses.

• Prototyping (rapid iteration before mass production).
• Custom medical implants (hip joints, hearing-aid shells, dental crowns).
• Hobbyist parts and replacement components.
• Food (chocolate, pasta — at the novelty end).
• Construction (whole-house concrete printing in some pilots).

Cambridge tip. Top-band candidates use the word ADDITIVE explicitly. Mark scheme rewards 'layer by layer', 'CAD model', 'extruded', and 'thermoplastic / filament' as a chain.

Sensors are input devices that capture physical quantities from the real world and convert them into digital signals the computer can process. Common sensors:

Sensor	Measures	Example use
Temperature	Heat	Heating control, glasshouse, fridge alarms
Light	Brightness	Auto-headlights, street lighting, photography
Pressure	Force per area	Burglar alarm under floor, tyre pressure
Motion / PIR	Movement / body heat	Intruder alarm, automatic lights
Sound	Sound level	Voice control, noise monitoring
Moisture / humidity	Water content	Glasshouse irrigation, hygrometers
pH	Acidity	Pool chemistry, hydroponics
Gas (CO, CO₂, smoke)	Air composition	Fire alarm, ventilation control
Infrared	Heat / proximity	Touchless taps, security

The control loop.

1. Sensor takes a reading.
2. Reading is converted to digital (via an ADC if the sensor is analogue).
3. Microprocessor compares the value to pre-set THRESHOLDS.
4. If outside the range, the microprocessor sends a signal to an ACTUATOR (motor, valve, heater) to bring it back.
5. Loop repeats.

Cambridge tip. Mark schemes love this five-step chain. Memorise it and adapt to whatever scenario the question gives (greenhouse, fish tank, oven, automatic doors, smart home).