Output Devices: Monitors, Printers, and Speakers

Output Devices

After a computer processes your request, it needs to communicate the result back to you. Without output devices, the computer would be solving every problem in complete silence — calculating perfectly, deciding correctly, and telling absolutely no one. A computer with no outputs is like a person who thinks brilliant thoughts but can never speak, write, or gesture. Useful to no one.

Output devices take the processed data — the numbers inside the CPU — and translate them back into a form humans can perceive: light, sound, physical print, vibration. They are the computer's voice.

What Makes Something an Output Device?

An output device receives processed data from the computer and presents it to the user. The direction of information flow is always from the CPU outward to the human world.

Monitor and Display

The monitor is the primary output device for almost every computer. It converts digital pixel data into visible light.

Display Technologies

LCD (Liquid Crystal Display) is the most widely used technology. An LCD panel works by shining a backlight (usually LED) through a layer of liquid crystals. Liquid crystals are molecules that can rotate the polarisation of light when an electrical voltage is applied. By controlling the voltage at each pixel, the display blocks or passes light, creating the image. A colour filter layer adds red, green, and blue sub-pixels.

OLED (Organic LED) takes a fundamentally different approach. Each pixel is a tiny organic compound that emits its own light when electricity passes through it. There is no backlight. This allows individual pixels to turn completely off — producing true, absolute black rather than the slightly grey black of an LCD. OLED displays have become standard on flagship smartphones and are increasingly common in monitors and laptops.

Resolution

Resolution describes how many pixels make up the image:

More pixels means more detail — but only if the content and the GPU can support it.

Refresh Rate and Response Time

Refresh rate (measured in Hz) is how many times per second the display updates its image. A 60 Hz monitor redraws the screen 60 times each second. Higher refresh rates make motion appear smoother:

• 60 Hz: standard, fine for office and general use
• 144 Hz: noticeable improvement in gaming and video
• 240 Hz: competitive gaming
• 360 Hz: professional esports

Response time measures how quickly a pixel transitions from one colour to another, measured in milliseconds. A slow response time creates ghosting — a blur trail behind fast-moving objects:

• 1 ms: gaming monitors (TN, fast IPS)
• 4–8 ms: typical office/professional IPS monitors

Panel Types and Colour

Professional content creators also care about colour gamut — the range of colours a display can reproduce:

• sRGB: the internet and Windows standard (~72% of visible colours)
• DCI-P3: cinema standard, ~25% wider than sRGB — used in photo and video editing
• Adobe RGB: print production standard

A monitor showing 99% DCI-P3 can display richer, more saturated colours than one showing only 72% sRGB. For casual use the difference is subtle; for a video editor delivering content for cinema, it is critical.

Printer

A printer converts digital documents into physical form on paper or other media.

Inkjet printers work by firing microscopic droplets of liquid ink from hundreds of tiny nozzles. The nozzles move across the paper, building the image line by line. Inkjet printers excel at reproducing continuous-tone photographs with smooth colour gradients. Print resolution is measured in DPI (Dots Per Inch) — consumer inkjet printers typically achieve 1,200–4,800 DPI for photo printing.

Laser printers use a completely different process: a laser beam draws the image onto a light-sensitive drum, which picks up dry toner powder. The drum rolls over the paper, transferring the toner, and a heat fuser melts it permanently into the fibre. Laser printers are faster and more economical for high-volume text printing, and the toner is waterproof and fade-resistant. Typical resolution: 600–1,200 DPI.

3D printers are additive manufacturing devices — they build three-dimensional objects by depositing material layer by layer. FDM (Fused Deposition Modelling) printers melt plastic filament and extrude it in precise patterns. Layer height typically ranges from 0.05 mm to 0.3 mm. A 3D printer is simultaneously an output device (it receives digital 3D model data from the computer) and a fabrication machine.

Speakers and Headphones

Sound is a pressure wave in air — molecules oscillating back and forth at frequencies the human ear perceives as pitch. Speakers and headphones must recreate those waves from a digital audio signal.

The process begins inside the computer with a DAC (Digital-to-Analog Converter) — a chip that converts the stream of digital audio samples (numbers) into a continuously varying electrical voltage, recreating the waveform of the original sound.

A speaker driver consists of:

1. A permanent magnet
2. A voice coil of wire attached to a paper or polymer cone
3. When the audio signal passes through the voice coil, it creates an electromagnet that is attracted to or repelled by the permanent magnet — moving the coil and cone back and forth
4. The moving cone pushes and pulls air, creating the sound waves you hear

Human hearing ranges from 20 Hz (the lowest rumble you can perceive) to 20,000 Hz (the highest treble). A speaker's frequency response specification describes the range of frequencies it can accurately reproduce. Hi-fi speakers and headphones aim for a flat response curve across as much of this range as possible.

Headphones place the drivers millimetres from your eardrum — which is why even a small headphone driver can produce powerful, accurate bass that would require a large subwoofer speaker.

Projector

A projector throws an image onto an external surface — a screen, wall, or ceiling. It functions like a monitor in reverse: instead of creating a self-contained lit display, it uses a powerful internal light source to project light outward.

Key specifications:

• Lumens: brightness. 2,000–3,000 lumens for dark rooms; 4,000+ lumens for bright environments
• Resolution: HD, FHD, 4K — same standards as monitors
• Throw ratio: the ratio of distance to image width. A 1.5:1 throw ratio means 1.5 metres of distance per 1 metre of image width
• Contrast ratio: the difference between the darkest and brightest the projector can produce

Modern laser projectors have largely replaced lamp projectors, offering 20,000+ hour lifespans versus 3,000–5,000 hours for traditional bulbs.

Haptic Feedback

Haptic output is the computer communicating through touch. A linear resonant actuator (LRA) — the type used in modern smartphones — is a small motor with a weighted mass suspended on a spring. Precise electrical pulses drive the mass back and forth at controlled frequencies, creating distinct tactile sensations.

Unlike an old "rumble" motor that simply vibrated continuously, a modern haptic engine can simulate the click of a physical button, the texture of dragging across gravel, or the pulse of a notification — entirely through controlled vibration. Apple's Taptic Engine and Android's advanced haptics use this technology.

In game controllers, HD Rumble (Nintendo) and DualSense Haptic Feedback (PlayStation 5) use similar actuators in the handles, allowing the sensation of rain, engine friction, or bowstring tension to be felt in the hands.

Complete Output Device Reference

A useful way to remember the difference between input and output: input devices are the computer's ears and eyes; output devices are its voice and hands. Together they complete the communication loop — the endless conversation between human intention and computational response that makes everything from watching a video to landing a spacecraft possible.