Input, Output and Storage Devices: Classification and Examples

Computer hardware uses peripheral devices to take in data, present results, and store information for later use. For Prelims revision, it is useful to classify these devices by their function and remember the most common examples and technologies behind them.

Classification of Input Devices

Input devices convert human-readable data into machine-readable form. They may be used for manual entry, direct data capture, audio-video input, or biometric authentication.

• Keyboard: Uses mechanical switches, membrane circuits, or capacitive sensors to enter alphanumeric and control codes.
• Mouse: Uses optical sensors or laser diodes to track movement and convert it into cursor coordinates.
• Trackball: Has a stationary base with a movable sphere, useful in space-constrained setups.
• Joystick and flight yoke: Convert multi-axis movement into directional input, especially in simulators and navigation systems.
• Stylus and graphics tablet: Use electromagnetic resonance to capture pen pressure, angle, and drawing vectors.
• Microphone: Converts sound vibrations into electrical audio signals.
• Webcam and digital camera: Use CCD or CMOS image sensors to capture light as pixels.
• Biometric scanner: Captures fingerprints, iris patterns, facial geometry, or vascular maps for identity verification.

Optical and Direct Data Capture Devices

These devices read printed, coded, or marked information directly from physical documents and objects.

• OMR (Optical Mark Recognition): Detects dark marks on pre-printed sheets by measuring light reflection.
• OCR (Optical Character Recognition): Converts scanned printed or handwritten text into editable machine text.
• Barcode reader: Uses red LED or laser light to decode black bars and white spaces, including UPC codes.
• QR scanner: Reads two-dimensional matrix barcodes using finder patterns in three corners.
• MICR (Magnetic Ink Character Recognition): Reads iron oxide ink characters printed on bank cheques.

Classification of Output Devices

Output devices convert processed digital data into human-readable or physical form. They include display units, printers, audio devices, and physical actuators.

• LCD: Uses liquid crystal molecules with backlighting to block or pass polarized light.
• LED display: Uses semiconductor diodes and is more energy efficient than traditional CCFL-based systems.
• OLED: Uses organic compounds that emit their own light, so no separate backlight is needed.
• CRT monitor: Uses focused electron beams and phosphor-coated screens to generate raster scan lines.
• Video projector: Projects digital images onto large surfaces using DLP micro-mirrors or 3LCD prisms.
• Speakers and headphones: Convert electrical audio signals into sound waves through electromagnetic voice coils and diaphragms.
• Haptic feedback actuator: Uses ERM motors or linear resonant actuators to simulate touch responses.
• CNC machines and 3D printers: Receive G-code instructions to manufacture physical objects or prototypes.

Printing and Hard-Copy Devices

Printers and plotters are important output devices used for paper copies and technical drawings.

• Impact printer: Creates impressions by striking an inked ribbon against paper using mechanical pins or character molds.
• Dot matrix printer: Uses a 9 to 24 pin printhead to form characters through patterns of dots.
• Inkjet printer: Sprays microscopic liquid ink droplets through thermal or piezoelectric nozzles.
• Laser printer: Uses a laser beam to form an electrostatic image on a photosensitive drum; toner is fused by heated rollers.
• Plotter: Uses pens, knives, or inkjet heads to draw continuous vector graphics for blueprints and engineering diagrams.

Classification of Storage Devices

Storage devices preserve programs, operating systems, and user data either temporarily or permanently. They are broadly divided into primary storage and secondary or tertiary storage.

• RAM (Random Access Memory): Volatile memory that loses stored bits when power is switched off.
• DRAM: Stores each bit in a capacitor-transistor pair and needs periodic refresh cycles.
• SRAM: Uses four to six transistors in a flip-flop configuration and is faster for cache access.
• ROM (Read-Only Memory): Non-volatile memory that stores boot firmware such as BIOS or UEFI.
• PROM: One-time programmable ROM.
• EPROM: Can be erased using ultraviolet light.
• EEPROM: Can be erased electrically.
• HDD (Hard Disk Drive): Records data as magnetic domains on spinning platters read by moving heads.
• SSD (Solid State Drive): Uses non-volatile flash memory chips without moving mechanical parts.
• NVMe: Uses the PCIe bus interface for faster data transfer.
• Magnetic tape: Used for long-term archival storage and cold backups.

RAM is volatile, while ROM is non-volatile. This is a common Prelims distinction.

Key Prelims Takeaways

• Input devices convert human-readable data into machine code.
• Output devices convert processed digital signals into readable or physical form.
• OMR reads marked answers; OCR reads printed or handwritten text.
• MICR is associated with bank cheques and magnetic ink characters.
• LCD, LED, OLED, and CRT are major display technologies.
• Laser printers use toner and fuser rollers; dot matrix printers use impact pins.
• RAM is volatile, while HDD, SSD, ROM, and magnetic tape are non-volatile storage options.