Understand output devices and their purposes

Output Devices – IGCSE 0478 (Section 3.2)

1. What is an Output Device?

An output device is any hardware that receives data from a computer and converts the digital information into a form that humans can perceive – visual, auditory or tactile.

2. Categories of Output Devices

2.1 Visual (Display) Devices

• Monitors (LCD, LED, OLED) – display text, graphics and video. Typical specs: size (inches), resolution (e.g., 1920 × 1080 px), refresh rate (Hz) and colour depth (bits per pixel).
• Projectors – enlarge a computer image onto a screen or wall. Key parameters: native resolution, brightness (lumens) and contrast ratio.
• VR/AR head‑sets – provide immersive visual (and often auditory) output. Look for per‑eye resolution, field‑of‑view and tracking type.

2.2 Printing Devices

• Inkjet printers – spray coloured ink; ideal for photos and low‑volume colour work. Typical DPI: 4800 × 1200.
• Laser printers – use a laser‑induced electrostatic image and toner; fast and economical for high‑volume monochrome or colour printing. Typical DPI: 1200 × 1200, speed 30 ppm (black).
• Dot‑matrix printers – impact printing; useful for multi‑part forms because they can print through several layers of paper.
• Plotters (vector printers) – draw lines with a moving pen; used for engineering drawings and large‑format graphics.

2.3 Audio Devices

• Speakers – output sound to the environment; characterised by power (W), frequency response (Hz) and connectivity (3.5 mm, HDMI, Bluetooth).
• Headphones / Ear‑buds – personal audio output; often include built‑in volume control and microphone.
• Sound cards (internal or external) – convert digital audio samples into analogue signals; support sampling rate and bit depth.

2.4 Tactile Devices

• Braille displays – refreshable cells that raise dots to represent Braille characters; assist visually impaired users.
• Haptic feedback units – provide vibration or force feedback in game controllers, smartphones and specialised training equipment.

2.5 Storage Devices Used as Output

• External hard‑disk drives, USB flash drives and optical discs (CD/DVD/BD) when data is written to them for later use (e.g., saved reports, backups).
• These are **secondary storage** devices that act as the final destination for output data.

3. Purposes of Output Devices (AO1 – Knowledge)

1. Present information in a readable, viewable or audible format.
2. Provide a permanent record (printed documents, saved files on storage media).
3. Facilitate communication and presentation (projectors, VR demos).
4. Assist users with disabilities (Braille displays, audio alerts, haptic cues).
5. Support interaction with virtual environments (VR head‑sets, haptic controllers).

4. Technical Characteristics (AO2 – Application)

4.1 Visual Devices – Resolution & Colour Depth

• Resolution – measured in pixels (e.g., 1920 × 1080) or PPI (pixels per inch) for monitors; higher values give finer detail.
• DPI (dots per inch) – used for printers; higher DPI yields sharper printed images.
• Colour depth – bits per pixel (e.g., 24‑bit = 16.7 million colours). Determines the range of colours that can be displayed or printed.

4.2 Printing Principles

• Raster printing – builds the page line‑by‑line (used by inkjet and laser printers).
• Vector printing – stores drawing commands (used by plotters and some specialised printers).

4.3 Audio Output – Sampling Rate & Bit Depth

• Sampling rate – how many times per second the analogue signal is sampled (e.g., 44.1 kHz for CD quality).
• Bit depth – number of bits for each sample (e.g., 16‑bit gives 65 536 amplitude levels).

4.4 Tactile Output – Refresh Rate & Dot Count

• Refreshable Braille cells typically have 40–80 positions per line and refresh at 10–20 Hz.
• Haptic actuators are rated by maximum force (N) and vibration frequency (Hz).

5. Choosing the Right Output Device (AO3 – Evaluation)

When selecting a device, weigh the following factors and justify your choice with reference to the task requirements.

6. Device Control – Connections, Drivers & Buffers

• Interfaces / ports: HDMI, DisplayPort, VGA (video); USB, Ethernet, Wi‑Fi (network printers); 3.5 mm jack, Bluetooth (audio).
• Device drivers: software that translates generic OS output commands into device‑specific instructions.
• Buffers: temporary storage (e.g., print spooler, audio buffer) that smooths data flow when the device’s speed differs from the CPU’s processing speed.

7. Data Flow – From CPU to Output Device

1. CPU processes data and stores the result in main memory (RAM).
2. Operating system forwards the data to the appropriate device driver.
3. The driver formats the data for the chosen interface (HDMI, USB, network).
4. Data may be placed in a buffer (print spooler, audio buffer) to match the device’s speed.
5. The output device receives the formatted data and converts it into a human‑readable form (image, sound, tactile pattern).

8. Practical Activity (Integrating AO2 & AO3)

Write a short program (e.g., in Python or Scratch) that prints a formatted report to a printer and then plays a confirmation sound.

1. Define the data to be printed (e.g., student scores).
2. Use appropriate output commands (print() for text, a library call for printing).
3. Trigger an audio alert using a sound‑play function.
4. Test the program with at least two different printers (inkjet and laser) and record any differences in speed or quality.
5. Evaluate which printer is more suitable for the task, citing cost, speed, DPI and environmental impact (AO3).

9. Comparison of Common Output Devices

10. Links to Other Syllabus Areas (Ensuring Full Coverage)

• Data Representation (Topic 1) – colour depth, sampling rate and DPI are direct applications of binary representation of images and sound.
• Data Transmission (Topic 2) – understand how HDMI, USB and network protocols move output data from the CPU to the device.
• Hardware Architecture (Topic 3) – recognise the role of the graphics processing unit (GPU) and sound card in preparing output.
• Software (Topic 4) – drivers and operating‑system buffering illustrate the software layer that controls output devices.
• Algorithms & Programming (Topics 7‑10) – writing programs that generate output (e.g., print statements, audio playback) develops procedural thinking and testing skills.
• Databases (Topic 10) – query results are often exported as printed reports or CSV files stored on external media.
• Boolean Logic & Logic Gates (Topic 9) – the internal circuitry of output devices uses logic gates to convert binary signals into analogue form.

11. Summary

Output devices translate digital information into visual, auditory or tactile signals that humans can perceive. Knowing the categories, technical specifications (resolution, DPI, sampling rate, colour depth), control mechanisms (ports, drivers, buffers) and practical considerations (cost, quality, accessibility) enables learners to:

• Identify the most appropriate device for a given task (AO1).
• Apply knowledge to configure and use devices in programmes (AO2).
• Evaluate alternatives in terms of performance, cost and user needs (AO3).