C. Computer Environments and Systems · Computer Environments and Systems

Peripheral Devices: Monitors, Printers, Scanners and More

C1.3About 65 minutes

Learning goals

I can sort peripherals into input, output and storage devices.
I can explain the key specifications of monitors, printers, scanners, keyboards, mice, speakers and USB flash drives.
I can calculate screen pixel counts, scan file sizes and printing costs from specifications.
I can recommend peripherals that match a user's needs, including accessibility needs.

Words to know

peripheral
A device outside the main computer that connects to it, such as a monitor, printer or keyboard.

input / output device
An input device sends data into the computer (keyboard, mouse, scanner, microphone). An output device presents data from the computer (monitor, printer, speakers).

resolution (screen)
The number of pixels across and down, such as 1920 × 1080.

refresh rate
How many times per second a monitor redraws the picture, in hertz (Hz).

dpi (dots per inch)
How many dots a printer prints, or a scanner samples, in each inch. Higher dpi shows finer detail.

ppm (pages per minute)
A printer's speed rating.

USB
Universal Serial Bus: the standard connector and bus for most peripherals. Versions differ in speed (USB 2.0 is 480 Mbps; USB 3.0, also called USB 3.2 Gen 1, is 5 Gbps).

assistive technology
Hardware or software that helps people with disabilities use a computer, such as screen readers, switch devices and alternative keyboards.

Everything outside the box

Your computer cannot do anything useful until something gets data into it and something gets results out. A peripheral is any device outside the main system that connects to it: by a cable (USB, HDMI, DisplayPort) or wirelessly (Bluetooth, Wi-Fi).

Peripherals come in three groups:

Input devices send data into the computer: keyboard, mouse, scanner, microphone, webcam, game controller.
Output devices present data from the computer: monitor, printer, speakers, headphones.
Storage devices do both: a USB flash drive or external drive saves data and gives it back.

A touchscreen is both input and output. Like internal parts, every peripheral has specs, and the right choice depends on who will use it and for what.

Data flows into the computer from input devices and out to output devices. A storage device such as a USB flash drive moves data both ways.

Monitors

Size: measured diagonally, in inches (even in Canada, monitor sizes are sold in inches).
Resolution: pixels across × pixels down. Common ones: 1920 × 1080 (Full HD, 1080p), 2560 × 1440 (QHD, 1440p) and 3840 × 2160 (4K UHD). More pixels mean sharper text and more room for windows side by side, which programmers love.
Refresh rate: how many times per second the picture is redrawn. 60 Hz is standard; gamers often want 144 Hz or more for smoother motion. At 60 Hz each frame lasts 1 ÷ 60 s ≈ 16.7 ms.
Response time: how quickly pixels change colour (in ms; lower is better for games).
Colour accuracy: often given as the percentage of a colour range such as sRGB that the screen can show. It matters for photographers and designers.
Ports: HDMI, DisplayPort or USB-C. The computer's video output must match (or use an adapter).

Three common screen resolutions drawn to the same scale. Doubling both the width and the height multiplies the number of pixels by 4, which is why 4K needs a much more powerful GPU to run games smoothly.

Printers and scanners

Printers. An inkjet sprays tiny drops of liquid ink; it is good at colour photos and cheap to buy, but ink can be expensive per page. A laser printer fuses powdered toner onto paper with heat; it is fast, sharp for text and cheaper per page for large volumes. Specs: speed (ppm), print resolution (dpi), colour or black-and-white only, duplex (prints both sides automatically, which saves paper), connectivity (USB, Wi-Fi), and cost per page (cartridge price ÷ pages it prints).

Scanners turn paper or photos into digital images. A flatbed scanner has a glass bed for books and photos; a sheet-fed scanner or automatic document feeder (ADF) pulls in stacks of pages. Specs: optical resolution (dpi), colour depth (bits per pixel), and speed. A higher dpi gives more detail, but the file size grows with the square of the dpi: doubling the dpi makes four times as many pixels.

Scanning text at about 300 dpi is usually plenty; old photos you want to enlarge may need 600 dpi or more.

def scan_size_mb(width_in, height_in, dpi, bytes_per_pixel=3):

pixels = (width_in * dpi) * (height_in * dpi)

return pixels * bytes_per_pixel / 1_000_000

print("Letter page at 300 dpi:", scan_size_mb(8.5, 11, 300), "MB")

print("4 x 6 photo at 600 dpi:", scan_size_mb(4, 6, 600), "MB")

Uncompressed size of a full-colour scan (3 bytes per pixel: one each for red, green and blue). File formats such as JPEG and PDF compress this a lot. Output (one line each): Letter page at 300 dpi: 25.245 MB / 4 x 6 photo at 600 dpi: 25.92 MB

Keyboards, mice, speakers and USB flash drives

Keyboard: wired (USB) or wireless (Bluetooth or a USB receiver); layout (in Canada you will see the Canadian Multilingual Standard and Canadian French layouts as well as the US layout); key type (mechanical keys last longer and give a clear click; membrane keys are quieter and cheaper); ergonomic shapes reduce wrist strain.
Mouse: sensitivity in dpi (also called CPI: how far the pointer moves for each inch the mouse moves), wired or wireless, number of buttons, and shape (ergonomic or vertical mice help some people avoid wrist pain).
Speakers and headphones: power in watts, and frequency response (the range of pitches they can play; human hearing covers roughly 20 Hz to 20 000 Hz). A microphone headset matters for online classes.
USB flash drive: capacity (GB) and speed, which depends on both the USB version and the drive's own read and write speeds. Its small size is handy but also makes it easy to lose, so do not keep your only copy of anything on one.

Accessibility. Peripherals help everyone use a computer. People who are blind or have low vision may use a screen reader with headphones or a refreshable braille display; people with limited hand movement may use switch devices, eye-tracking, voice input or an alternative keyboard. A good recommendation always asks about the user's needs.

Worked example

Example 1: Which printer costs less?

The Lin family prints about 150 pages a month, almost all homework in black and white. Printer A (inkjet): $90, black cartridge $35 lasts 250 pages. Printer B (laser): $180, toner $90 lasts 3000 pages. Compare the cost over two years.

Pages in two years: 150 × 24 = 3600 pages.
Cost per page: A: $35 ÷ 250 = $0.14. B: $90 ÷ 3000 = $0.03.
Printing cost over two years: A: 3600 × $0.14 = $504. B: 3600 × $0.03 = $108. (Both printers usually come with a starter cartridge; we ignore that to keep it fair.)
Total with the printer price: A: $90 + $504 = $594. B: $180 + $108 = $288.

Printer B (laser) costs about $306 less over two years. The cheaper printer to buy is the more expensive one to own.

Worked example

Example 2: Matching peripherals to a user

Jordan is starting a co-op placement doing graphic design and will also edit podcasts. Recommend a monitor and an audio peripheral, naming the specs that matter.

Graphic design needs accurate colour and sharp detail: choose a monitor with high colour accuracy (close to 100% sRGB) and at least 2560 × 1440 resolution. Refresh rate matters less; 60 Hz is fine.
Podcast editing needs to hear sound accurately: closed-back headphones (or studio monitor speakers) with a wide, flat frequency response, plus a USB microphone or audio interface for recording.
Connection check: the computer's video output (HDMI, DisplayPort or USB-C) must match the monitor's input.

A colour-accurate 1440p (or 4K) monitor and good headphones with a wide frequency response, chosen because of Jordan's tasks, not the biggest numbers.

Just for fun

The first computer mouse, built in the 1960s by Douglas Engelbart's team, had a wooden case and two metal wheels instead of a ball or a laser. It also had a cord coming out of the back, which is how the "mouse" got its tail and its name.

Hands-on activity

Peripheral survey at home

You need: a computer and any peripherals in your home (monitor, printer, keyboard, mouse, headphones, flash drive). Do not unplug anything that someone else is using, and ask a grown-up before moving a printer or monitor.

Make a table with columns: device, input/output/storage, how it connects (USB, HDMI, Bluetooth, Wi-Fi), and two specs.
Find specs on the device's label (usually underneath or on the back) or in the computer's settings. Display settings show the screen resolution and often the refresh rate.
Use the scan-size program above to work out the uncompressed size of a scan of one of your school pages at 150, 300 and 600 dpi. What happens to the size each time the dpi doubles?
Choose one device that does not suit its user well (for example, a small monitor for someone who programs) and write a one-paragraph recommendation for a replacement, naming the specs.

What to look for: correct classification (a headset with a microphone is both input and output), real specs with units, and the observation that doubling the dpi multiplies the scan size by 4 (about 6.3 MB, 25.2 MB and 101.0 MB for a letter page).

Your turn

Classify each as input, output or both: webcam, printer, touchscreen, microphone, speakers.

How many pixels does a 2560 × 1440 monitor have?

A monitor runs at 144 Hz. How long is each frame shown, to the nearest tenth of a millisecond?

Why does a 600 dpi scan of a photo take four times the space of a 300 dpi scan?

Give two specs to compare when choosing a printer for a family that prints a lot of homework.

Name one peripheral that helps a person who is blind use a computer, and what it does.

More practice: warm-up

What does "Hz" measure on a monitor?

What do the letters dpi stand for?

Is a USB flash drive an input, output or storage device?

Which printer type uses powdered toner?

How is monitor size measured?

More practice: on your own

How many times more pixels does a 3840 × 2160 screen have than a 1920 × 1080 screen? Show your work.

A laser printer prints 30 ppm. How long will a 75-page report take?

A gamer has a 165 Hz monitor connected through an old cable that only supports 60 Hz at that resolution. What will happen?

Find the uncompressed size of a 5 × 7 inch photo scanned at 400 dpi with 3 bytes per pixel.

A teacher wants a keyboard for typing in French and English. What should she look for?

Challenge

A 27-inch monitor has a resolution of 2560 × 1440. Find its pixel density in pixels per inch (ppi), to one decimal place. (Hint: use the Pythagorean theorem on the pixel counts.)

Printer C costs $120 and $0.05 per page; Printer D costs $60 and $0.11 per page. After how many pages do they cost the same? Which is cheaper for a family printing 1500 pages a year?

Write a Python function frame_ms(hz) that returns the time per frame in milliseconds, rounded to 1 decimal place, and show what print(frame_ms(60), frame_ms(240)) prints.

Check your understanding

Quiz

Which of these is an input device?

How many pixels does a 1920 × 1080 screen have?

What does a monitor's refresh rate measure?

A scan is made at 600 dpi instead of 300 dpi. About how much larger is the uncompressed file?

Which spec matters most when comparing the long-term cost of two printers?

A photographer is choosing a monitor. Which spec matters most for her work?

For parents and teachers

Big idea: Expectation C1.3 asks students to relate the specifications of common peripherals (printer, monitor, scanner, keyboard, mouse, speakers, USB flash drive) to user requirements.

How to help: Walk around the house with your teen and identify every peripheral and how it connects. When you next shop for a printer or monitor, let your teen do the comparison and present it to you with the specs that matter. If anyone in the family uses assistive technology, talk about how it was chosen.

Common difficulties:

Thinking a bigger number is always better (a 240 Hz monitor is wasted on someone writing essays).
Forgetting that pixel counts and scan sizes grow with the square of the linear size or dpi.
Ignoring running costs (ink and toner) and only comparing purchase prices.
Not checking that connectors and cables support the desired speed or refresh rate.