Study notes
Input devices
Input devices send data and instructions into the computer.
| Device | Use / key fact |
|---|
| Keyboard | QWERTY layout; standard desktop keyboard has 12 function keys (F1–F12) |
| Mouse | Pointing device invented by Douglas Engelbart; optical mice use an LED/laser sensor |
| Trackball | Stationary pointer; user rolls the ball on top |
| Touchpad | Laptop pointing surface |
| Joystick | Games, simulators, cranes |
| Light pen / stylus | Draws or selects directly on screen |
| Scanner | Converts paper documents and photos into digital images |
| Digitizer / graphics tablet | Converts hand drawings and signatures into digital form |
| Microphone, webcam | Sound and video input |
| Biometric scanner | Fingerprint, iris, face (Aadhaar authentication, attendance) |
Recognition devices (very important for banking)
| Short form | Full form | Where used |
|---|
| MICR | Magnetic Ink Character Recognition | Cheque processing in banks; font E-13B; the 9-digit MICR code identifies city, bank and branch |
| OMR | Optical Mark Reader / Recognition | Evaluating bubble answer sheets of objective exams |
| OCR | Optical Character Recognition | Converting scanned printed text into editable text |
| BCR | Bar Code Reader | Retail billing; reads parallel lines (1D) with light; QR codes are 2D |
| RFID | Radio Frequency Identification | FASTag toll collection, library and inventory tags |
Output devices
- Monitor – CRT (old), LCD, LED, OLED. The smallest dot on screen is a pixel (picture element). Resolution 1920 × 1080 = Full HD. Refresh rate is measured in hertz (Hz).
- Printer – hard copy output.
- Plotter – large engineering drawings, maps, blueprints (CAD).
- Speaker / headphones – sound output.
- Projector – displays screen output on a large surface.
Printers
| Type | How it prints | Examples |
|---|
| Impact | Strikes an inked ribbon against paper; noisy; can print carbon copies | Dot-matrix, daisy-wheel, line (chain, drum, band) printers; bank passbook printers |
| Non-impact | No striking; quiet and high quality | Laser (toner + drum), inkjet (sprays ink droplets), thermal (heat-sensitive paper, ATM slips and bills) |
- Dot-matrix speed: CPS (characters per second).
- Line printer speed: LPM (lines per minute).
- Laser/inkjet speed: PPM (pages per minute).
- Print quality (resolution): DPI (dots per inch).
Devices that are both input and output
Touch screen (displays and senses touch), headset with microphone, modem and network card (send and receive data), and multifunction printers with scanners.
Keyboard key groups
- Toggle keys: Caps Lock, Num Lock, Scroll Lock – press once to switch on, again to switch off.
- Modifier keys: Shift, Ctrl, Alt, Windows key – used in combination with other keys.
- Function keys: F1 (help) to F12.
- Navigation keys: arrows, Home, End, Page Up, Page Down.
Ports and connectors
| Port | Used for |
|---|
| USB (Universal Serial Bus) | Most peripherals; USB-C is reversible |
| HDMI | High-Definition Multimedia Interface – digital audio and video |
| VGA | Older analog video connector |
| RJ-45 | Ethernet network cable |
| RJ-11 | Telephone line / dial-up modem |
| PS/2 | Old keyboard and mouse connector |
Display technologies at a glance
| Technology | Key point |
|---|
| CRT (Cathode Ray Tube) | Old, bulky monitors using an electron gun |
| LCD (Liquid Crystal Display) | Flat panel; needs a backlight |
| LED monitor | LCD panel lit by LEDs; thinner and more power-efficient |
| OLED | Each pixel produces its own light; deep blacks; used in premium phones |
Screen size is measured diagonally in inches. Higher resolution means more pixels and a sharper picture; a higher refresh rate (60 Hz, 120 Hz) gives smoother motion. A graphics card (GPU) generates the image signal sent to the monitor.
Exam tip: "Cheque" means MICR, "answer sheet" means OMR, "scanned text to editable text" means OCR, "supermarket" means barcode reader.