A computer needs a way to take things in and a way to give results back. Input devices carry data and instructions into the computer, like a keyboard, mouse or scanner. Output devices bring results out in a form people can use, like a monitor, printer or speaker. Some devices, like a touchscreen, do both. Devices attached from outside are called peripherals. Punjab Police papers ask to sort devices into these groups, and about printers, OCR, OMR and MICR.
3
Groups of devices
Input, output, both
F1–F12
Function keys
A separate group from control keys
9
Digits in a cheque's MICR code
City, bank, branch
2
Families of printers
Impact and non-impact
Input, output, or both?
The one question behind half the papers.
WHERE EVERY DEVICE FITS
- inInput unitTakes data from the outside world into the computer.
- CPU and memoryProcess the data in machine form (0s and 1s).
- outOutput unitGives results to the outside world in a human-acceptable form.
| Input only | Output only | Both input and output |
|---|---|---|
| Keyboard, mouse, trackball, joystick | Monitor (VDT / VDU) | Touchscreen |
| Scanner, barcode reader, OCR, OMR, MICR | Printer, plotter | Headset with a microphone |
| Microphone, webcam, camera | Projector, speaker | — |
| Light pen, touchpad, fingerprint scanner | Headphones | — |
Port
USB
Universal Serial Bus. Connects keyboards, mice, printers and pen drives.
Port
HDMI
Carries video and sound to a monitor, TV or projector.
Wireless
Bluetooth
Short-range radio link for wireless mice, keyboards and headsets.
Each device also needs a small program called a device driver so the operating system can use it.
QUICK CHECK
The ______ enables a computer system to supply information to outside world in human acceptable form.
Tap an option to answer
Answer: D — output unit
Punjab Police SI, 2022. Supplying results to the outside world is the output unit's job. The input unit does the opposite.
QUICK CHECK
Which of the following is NOT an output device?
Tap an option to answer
Answer: A — Keyboard
Punjab Police Constable, 2021. A keyboard only sends data in. Projector, monitor and plotter all give output.
QUICK CHECK
Which of the following is classified as both an input and output device?
Tap an option to answer
Answer: A — Touchscreen
Punjab Police Constable, 2025. A touchscreen senses touch (input) and shows the display (output). A monitor only shows; a scanner only reads.
Keyboard, mouse and other pointing devices
Key groups, mouse actions, joystick and light pen.
| Key group | Keys |
|---|---|
| Typing (alphanumeric) | Letters, numbers, Space, Enter, Backspace |
| Control keys | Ctrl, Alt, Esc, Windows key |
| Function keys | F1 to F12 (F1 = Help in most programs; F2 = Rename in File Explorer) |
| Navigation keys | Arrow keys, Home, End, Page Up, Page Down |
| Toggle keys | Caps Lock, Num Lock, Scroll Lock (press once on, once off) |
| Numeric keypad | The calculator-style block on the right |
| Mouse action | What it does |
|---|---|
| Click (left, once) | Selects an item |
| Double click | Opens a file, folder or program |
| Right click | Opens the shortcut (context) menu |
| Drag and drop | Hold the button, move, then release to move an item |
| Scroll | Turn the wheel to move up or down a page |
More pointing devices
Joystick: a stick that tilts in any direction. Used for games and simulators.
Evan-Amos, Wikimedia Commons · Public domain
Light pen: a light-sensitive pen used to pick objects on the screen.
Dgb32, Wikimedia Commons · CC BY 4.0
Most popular
Mouse
The most popular point-and-draw device on desktops. Invented by Douglas Engelbart in the 1960s.
Ball on top
Trackball
Like an upside-down mouse. You roll the ball with your thumb or fingers.
Laptops
Touchpad
A flat pad that follows your finger.
Drawing
Graphics tablet / stylus
A pen and pad for drawing and handwriting.
QUICK CHECK
______ is the most popular point-and-draw device generally used in Desktop computers.
Tap an option to answer
Answer: B — Mouse
Punjab Police SI, 2021. Every desktop comes with a mouse. A trackball also points, but it is a niche device.
QUICK CHECK
Which of the following is an action that can be performed with a mouse? I. Double click II. Drag and drop
Tap an option to answer
Answer: A — Both I and II
Punjab Police SI, 2021. Double click opens items; drag and drop moves them. Both are standard mouse actions.
QUICK CHECK
Which of the following is not a control key of a computer keyboard?
Tap an option to answer
Answer: C — F2
Punjab Police SI, 2023. Alt, Ctrl and Esc are control keys. F2 belongs to the function keys F1–F12.
Scanners and reading machines: OCR, OMR, MICR, barcodes
Devices that read paper, marks, ink, bars and voices.
KEY TERM
Scanning makes a picture
A scanner shines light on a page and records it as a grid of dots (pixels). So a scanned document is stored as an image, not as editable text. To turn that image into text you can edit, you need OCR software.
Paper page→Scanner→Image→OCR → editable text
| Device | Full form | What it reads / where used |
|---|---|---|
| OCR | Optical Character Recognition | Printed or typed letters → editable text |
| OMR | Optical Mark Recognition (Reader) | Filled bubbles on answer sheets and forms |
| MICR | Magnetic Ink Character Recognition | Magnetic-ink numbers on bank cheques |
| Barcode reader | — | Black-and-white bars on products, at billing counters |
| QR code scanner | Quick Response code | Square 2-D codes, e.g. UPI payments by phone camera |
| Biometric scanner | — | Fingerprint, face or iris, e.g. attendance machines |
- Microphone: takes sound in. Speech recognition takes audio (your voice) as input and turns it into text or commands.
- Webcam / digital camera: take pictures and video in.
QUICK CHECK
Scanned input document is stored as ______ instead of editable text.
Tap an option to answer
Answer: B — image
Punjab Police SI, 2021. A scanner records a picture of the page. The page shows text, but the file is an image until OCR is used.
QUICK CHECK
__________ is an input device.
Tap an option to answer
Answer: C — Magnetic Ink Character Recognition
Punjab Police SI, 2022. MICR = Magnetic Ink Character Recognition. It reads cheque numbers into the computer. The other three swap one word.
QUICK CHECK
What type of an input does the speech recognition device take?
Tap an option to answer
Answer: A — Audio
Punjab Police Constable, 2021. Speech is sound, so the input is audio. Text is what it may produce, not what it takes in.
Monitors, projectors and speakers
Output you see or hear: soft copy.
KEY TERM
Monitor (VDT / VDU)
The monitor is the main output device. It is also called a VDT (Video Display Terminal) or VDU (Visual Display Unit). The picture is made of tiny dots called pixels. More pixels (higher resolution, like 1920 × 1080) means a sharper picture.
Pixel→Resolution→Sharp picture
Output only
Projector
Throws the screen image onto a wall for a whole room. The most common presentation equipment.
Output only
Speakers / headphones
Turn the computer's signal into sound.
Both
Touchscreen
A display that also senses touch. It is an input device too.
Microphone, camera and OCR bring data in. The projector is the output device among them.
QUICK CHECK
What is the full form of VDT?
Tap an option to answer
Answer: C — Video Display Terminal
Punjab Police Constable, 2021. VDT = Video Display Terminal, another name for a monitor. Each wrong option changes one word.
QUICK CHECK
Which of the following can work only as an output device?
Tap an option to answer
Answer: C — Projector
Punjab Police SI, 2021. A projector only sends the picture out. A touch screen is both; scanner and trackball are input.
QUICK CHECK
Which one is the most common presentation equipment?
Tap an option to answer
Answer: C — Projector
Punjab Police SI, 2021. A projector shows slides to a whole room. OMR and OCR are input; a plotter prints large drawings.
Printers and plotters: hard copy
Impact vs non-impact, and every printer the papers name.
An impact printer and a non-impact printer
Dot matrix printer (24-pin): pins strike an inked ribbon. Impact.
Corvair, Wikimedia Commons · CC BY-SA 4.0
Inkjet printer, covers off: tiny ink drops are sprayed. Non-impact.
Snewkirk7953, Wikimedia Commons · CC BY-SA 3.0
IMPACT PRINTERS (STRIKE THE PAPER)
- Dot matrix: character printer, pins and ribbon
- Daisy wheel: character printer, a wheel of letters
- Drum and chain printers: line printers, a whole line at a time
- Noisy, but can print carbon copies
NON-IMPACT PRINTERS (NO STRIKING)
- Inkjet: sprays tiny drops of ink
- Laser: page printer; uses toner and a drum, like a photocopier
- Thermal: heat on special paper, e.g. shop receipts
- Quiet, good for graphics; cannot make carbon copies
| Printer | Prints | Speed measured in |
|---|---|---|
| Character printer (dot matrix, daisy wheel) | One character at a time | cps: characters per second |
| Line printer (drum, chain) | One line at a time | lpm: lines per minute |
| Page printer (laser) | A whole page at a time | ppm: pages per minute |
KEY TERM
Plotter
A plotter is an output device for large drawings: building plans, engineering designs, maps and big charts. It gives hard copy, like a printer, but on very large sheets.
CAD design→Plotter→Large sheet
QUICK CHECK
Which of the following statement is true about dot matrix printer? I. Non-impact printer II. Produces carbon copies III. Character printer
Tap an option to answer
Answer: B — II and III
Punjab Police SI, 2022. Its pins strike the paper, so it is an impact printer and statement I is false. Striking is also why it can make carbon copies.
QUICK CHECK
A ______ is the most widely used device for obtaining output in physical form.
Tap an option to answer
Answer: D — Printer
Punjab Police SI, 2023. Physical output = hard copy on paper = printer. Monitor and projector give soft copy; a scanner is input.
QUICK CHECK
A document or image stored on the hard disk or a pen drive is referred to as a ______.
Tap an option to answer
Answer: A — soft copy
Punjab Police SI, 2023. An electronic file is a soft copy. "Hard" in hard disk tempts you towards hard copy, which means paper.
Quick revision
Full forms, traps and one-line facts.
FLASHCARDS
Full forms: tap to check
- OCR
- Optical Character Recognition
- OMR
- Optical Mark Recognition
- MICR
- Magnetic Ink Character Recognition
- VDT
- Video Display Terminal
- VDU
- Visual Display Unit
- CRT
- Cathode Ray Tube
- LCD
- Liquid Crystal Display
- LED
- Light Emitting Diode
- USB
- Universal Serial Bus
- HDMI
- High-Definition Multimedia Interface
- QR code
- Quick Response code
- cps / ppm
- Characters per second / Pages per minute
COMMON TRAPS
- Touchscreen = both input and output. A plain monitor is output only.
- Projector = output only. OCR, OMR, scanner, microphone, camera = input.
- Dot matrix is IMPACT, even though it prints dots.
- F1–F12 are function keys, not control keys.
- A scanned page is an image until OCR turns it into text.
Also asked onceTap to open
- A light pen uses a light-sensitive detector to choose objects on a display screen.
- Both double click and right click are ways of entering instructions through the mouse.
- Among microphone, camera, projector and OCR, the projector is the output device.
- Among printer, projector, speaker and touch screen, the touch screen is the input device.
- Memory-mapped I/O: devices share the same addresses as main memory, so its main drawback is less address space for main memory. The other way, separate I/O ports, keeps device addresses apart.
CHECK YOURSELF
Sort these into input, output or both: scanner, plotter, touchscreen, MICR, projector, microphone.
Show answer
Input: scanner, MICR, microphone. Output: plotter, projector. Both: touchscreen.