CSS Computer Science (Optional) — Paper-I, Section-A, Topic I, p.12. Covers: Input & Output Devices and Their Types.
Classification Principle
Devices are classified by the direction of data flow relative to the computer:
- Input devices: data flows into the computer (from the outside world/user to the system)
- Output devices: data flows out of the computer (from the system to the outside world/user)
- Both (I/O) devices: some devices perform both roles simultaneously
Broad Types of Input
- Text-based input: keyboard
- Pointing/selection input: mouse, joystick, touchpad
- Image/optical input: scanner, digital camera, barcode reader
- Audio/video input: microphone, webcam
- Direct data capture: touchscreen (captures touch position directly)
Broad Types of Output
- Visual output: monitor, projector
- Print output (hard copy): printer, plotter
- Audio output: speaker, headphones
Devices That Are Both Input and Output
- Touchscreen: a display that also acts as an input device — a sensor layer (resistive, or more commonly today capacitive) detects the position and pressure of a finger or stylus and reports it as input, while the same panel simultaneously shows the visual output. Found on smartphones, tablets, ATMs, and point-of-sale terminals; it gives an intuitive, hardware-free interface but can be less precise than a mouse for fine work and is prone to smudging/wear.
- Modem (Modulator-Demodulator): converts a computer's outgoing digital data into a signal suitable for transmission over a communication line (modulation) and converts an incoming signal back into digital data (demodulation) — so it is simultaneously an output device (sending) and an input device (receiving). Dial-up modems worked over telephone lines; today's broadband/cable and fibre modems perform the same input/output role at far higher speed.
- Network Interface Card (NIC): the adapter (built-in or plug-in) that lets a computer physically join a wired (Ethernet) or wireless (Wi-Fi) network; it is bidirectional because it must both transmit outgoing packets (output) and receive incoming packets (input), each identified by the card's unique hardware MAC address.