Input and output devices — Computer Science

In this lesson you will learn

sort devices into input, output, both input and output, and processing (memory) devices
assign keyboard keys to DİM’s groups and explain what keys such as Backspace and Delete do
calculate a monitor’s number of pixels, its diagonal in centimetres and a printer’s printing time
solve “choose the true (false) statements” tasks

You press the A key and the letter “a” appears on the screen. At that moment three devices are at work: the keyboard sends a signal to the computer, the processor handles it, and the monitor shows the result. Devices that bring information into the computer and take it out act as “translators” between people and the computer. Every one of DİM’s four entrance exams of 2025–2026 had a task on computer hardware, and two of them asked about the key groups.

Input, processing, storage and output

Computer devices are grouped by the job they do. The processor and memory are inside the system unit (they are studied in the lesson “Inside the computer: processor, memory and motherboard”); the other devices are peripherals: they are connected to the computer by cable or wirelessly.

Definition

Input device

A device that brings information into the computer, turning signals from people and the world into code the computer understands: keyboard, mouse, scanner, microphone, webcam.

Definition

Output device

A device that takes the results of the computer’s work out in a form people can perceive — picture, text, sound: monitor, printer, plotter, projector, speakers.

Input devices	Output devices	Both input and output
keyboard	monitor	touchscreen
mouse, touchpad	printer	multifunction device (printer + scanner + copier)
scanner, barcode reader	plotter	headset (headphones with a microphone)
microphone	projector	interactive whiteboard
webcam, digital camera	speakers, headphones
joystick, graphics tablet, sensors

Interactive

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The keyboard and its key groups

A standard keyboard has more than 100 keys. Their layout is called QWERTY after the first six letters of the top letter row; to type in Azerbaijani, the Azerbaijani keyboard layout is chosen in the operating system, and then letters such as ı, ö, ü, ğ, ç, ş and the schwa can be typed too. In the school textbook and in DİM tasks the keys are divided into groups by the job they do:

Group	Keys	What they are for
Function	`F1` … `F12`	programs give them jobs: `F1` — help, `F2` — rename, `F5` — refresh
Service (control)	`Esc`, `Tab`, `Caps Lock`, `Shift`, `Ctrl`, `Alt`, `Insert`, `Delete`, `Backspace`, `Enter`	control the working mode, confirm or cancel a command, edit text
Cursor control	`←` `↑` `→` `↓`, `Home`, `End`, `PgUp`, `PgDn`	move the cursor through the text and the screen
Alphanumeric	letters, digits, signs, space	typing text
Numeric keypad	digits and `+ − * /` on the right, `Num Lock`	typing numbers quickly

In real DİM tasks: Caps Lock, Alt, Insert, Shift, Esc — service; F1 — function; Home, End, PgUp, PgDn — cursor control keys.

deletes the character to the left of the cursorBackspace

deletes the character to the right of the cursorDelete

switches between insert and overwrite modesInsert

turns capital-letter mode on and offCaps Lock

while held, types a capital letter or the upper sign of a keyShift

moves the cursor to the start of the lineHome

moves the cursor to the end of the lineEnd

copies the selection to the clipboard (Ctrl+V pastes it)Ctrl+C

A matching task

Match the groups and the keys.
1. function 2. service 3. cursor control
a. Esc b. End c. F7 d. Ctrl e. PgDn
A) 1 – c; 2 – a, d; 3 – b, e
B) 1 – c, d; 2 – a; 3 – b, e
C) 1 – a; 2 – c, d; 3 – b, e
D) 1 – c; 2 – b, d; 3 – a, e
E) 1 – c; 2 – a, e; 3 – b, d

Show solution

F7 starts with F — function (1 – c).
Esc cancels a command, Ctrl gives commands together with other keys — both are service keys (2 – a, d).
End takes the cursor to the end of the line, PgDn one screen down — cursor control (3 – b, e).
Answer: A) 1 – c; 2 – a, d; 3 – b, e.

Backspace and Delete

The screen shows the word informatika; the cursor stands after inform, between m and a. First Backspace is pressed 2 times, then Delete 3 times. What word remains?

Show solution

Backspace deletes the characters to the left of the cursor: m, then r → info|atika (| is the cursor).
Delete removes those on the right: a, t, i → info|ka.
Answer: infoka.

Interactive

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Other input devices

A mouse moves the pointer on the screen; modern mice are optical or laser, and many are wireless. A laptop has a touchpad instead. A touchscreen senses the touch of a finger and shows the picture at the same time, so it is both an input and an output device. A microphone brings sound into the computer, a webcam and a digital camera bring pictures. Games use a joystick and artists a graphics tablet; in smart devices temperature, light and motion sensors collect data from the world around.

Definition

Scanner

An input device that turns text or a picture on paper into a digital image and brings it into the computer. Kinds: flatbed (the document lies on a glass plate), handheld (moved over the surface by hand), drum (for high-quality print work), sheet-fed (pulls the pages in by itself), as well as barcode and 3D scanners. Its quality is measured in dpi — dots per inch.

Output devices: monitor, printer, plotter

A monitor’s picture is made of tiny dots — pixels. The number of pixels across and down is the resolution, for example 1920 × 1080 (Full HD). The size of a screen is given by the length of its diagonal in inches (1 inch = 2.54 cm). The picture is refreshed many times a second: a refresh rate of 60 Hz means 60 times per second. Old cathode-ray tube (CRT) monitors have been replaced by liquid-crystal (LCD, with LED backlight) and OLED screens.

N = a · b

where:

Nthe number of pixels on the screen
a, bthe numbers of pixels across and down (resolution a × b)

The number of pixels is the product of the two numbers of the resolution.

Counting pixels

How many pixels are on the screen?
1) 1920 × 1080 (Full HD)
2) 1366 × 768
3) 3840 × 2160 (4K). How many times more than Full HD is it?

Show solution

1) N = 1920 · 1080 = 2,073,600 pixels (about 2 million).
2) N = 1366 · 768 = 1,049,088 pixels.
3) N = 3840 · 2160 = 8,294,400 pixels. 3840 = 2 · 1920 and 2160 = 2 · 1080, so it is 2 · 2 = 4 times more.

d (cm) = d (in) · 2.54

where:

dthe screen diagonal

To turn inches into centimetres, multiply by 2.54.

The diagonal in centimetres

1) A monitor’s diagonal is 24 inches. How many centimetres is that?
2) A laptop screen is 15.6 inches. What is it in centimetres (round to one decimal place)?

Show solution

1) 24 · 2.54 = 60.96 cm ≈ 61 cm.
2) 15.6 · 2.54 = 39.624 cm ≈ 39.6 cm.

Printers put information on paper. A dot-matrix printer strikes an inked ribbon with pins — it is noisy, but still used for multi-part forms. An inkjet printer sprays tiny drops of ink onto the paper, and a laser printer sticks powder (toner) to an image drawn by a laser beam and fixes it with heat; a 3D printer “builds” an object layer by layer. A printer’s speed is measured in pages printed per minute (ppm) and its quality in dpi. A plotter is an output device that draws large-format drawings, maps and posters; engineers and architects use it. A projector puts the picture on a big screen, while speakers and headphones output sound.

t = N / vt = N / v

where:

tprinting time, minutes
Nthe number of pages
vthe printer’s speed, pages per minute

When two printers work together, their speeds add up.

Printing time

1) How many minutes does a 30 ppm laser printer need for 240 pages?
2) How many minutes do a 12 ppm inkjet printer and a 36 ppm laser printer need together for 480 pages?

Show solution

1) t = 240 / 30 = 8 minutes.
2) Combined speed: 12 + 36 = 48 ppm. t = 480 / 48 = 10 minutes.

Choosing devices for a task

Leyla wants to copy her grandmother’s old paper photos into the computer, make a large family-tree chart from them, have it drawn on paper 1 m wide, and then show it to relatives on a video call while talking. Which devices does she need, and of what kind are they?

Show solution

Copying the photos — a scanner (input).
Drawing on paper 1 m wide — an ordinary printer cannot handle this size, so a plotter is needed (output).
The video call — a webcam and a microphone (input), a monitor and speakers or headphones (output); headphones with a microphone — a headset — are both input and output.

“Choose the true statements” tasks

DİM often tests hardware with five statements: you must pick the true (or the false) ones, and the answer options are pairs of numbers. Solve such a task in order:

1
Read the question carefully
Are the true or the false statements asked for? This word changes the answer completely.
2
Mark each statement T or F
Look at the key words: the device name and the verb (“brings in”, “takes out”, “processes”, “stores”).
3
Pick the option
Find the option that contains all the needed numbers and only them.

The false statements

Choose the false statements.
1. A plotter is an output device.
2. A scanner brings a paper image into the computer.
3. A monitor’s size is given by the length of its diagonal in inches.
4. A microphone is an output device.
5. A processor is an input device.
A) 1, 4 B) 4, 5 C) 2, 3 D) 3, 5 E) 1, 2

Show solution

1 — T (a plotter puts drawings on paper).
2 — T.
3 — T.
4 — F: a microphone brings sound into the computer; it is an input device.
5 — F: a processor is a processing device.
Answer: B) 4, 5.

Key points

Input devices bring information into the computer (keyboard, mouse, scanner, microphone, webcam); output devices take it out (monitor, printer, plotter, projector, speakers).
A touchscreen, a multifunction device and a headset are both input and output; the processor is a processing device, RAM and disks are storage devices.
Key groups: function (F1–F12), service (Esc, Tab, Caps Lock, Shift, Ctrl, Alt, Insert, Delete, Backspace, Enter), cursor control (arrows, Home, End, PgUp, PgDn), alphanumeric, numeric keypad.
Backspace deletes the character to the left of the cursor, Delete the one to the right.
Number of pixels N = a · b; 1 inch = 2.54 cm; printing time t = N / v, a printer’s speed is measured in pages per minute.

Check yourself

12 questions. Every correct answer earns XP.

1 / 12

Which device is an output device?