Output Devices: Display Technologies & Printer Mechanics (Impact vs Non-Impact)

• CRT (Cathode Ray Tube): Classic display using an electron gun firing focused electron beams onto a phosphor-coated screen inside an evacuated glass tube via magnetic deflection coils. • LCD (Liquid Crystal Display): Uses liquid crystal molecules sandwiched between two polarizing filters. A CCFL or LED backlight passes light through crystals whose molecular orientation is modulated by electrical voltage to control light transmission. • LED & OLED (Organic Light Emitting Diode): OLED displays use organic carbon-based semiconductor compounds that emit their own light when current passes through (self-emissive pixels). Delivers true infinite black contrast, wide viewing angles, and ultra-thin flexible screens. • Key Display Metrics: • Resolution: Total pixel grid count (e.g. Full HD: 1920x1080, 4K UHD: 3840x2160). • Refresh Rate: Times the image is redrawn per second (60 Hz, 144 Hz, 240 Hz). • Aspect Ratio: Proportional ratio of screen width to height (Standard: 16:9, Ultra-wide: 21:9). • Dot Pitch: Physical distance between adjacent sub-pixel phosphor centers (smaller dot pitch = sharper image).

Printers are classified primarily by whether the printing mechanism physically strikes the paper: 1. Impact Printers (Mechanical Strike Mechanism): • Principle: Print characters by physically striking an inked ribbon against paper using pins, hammers, or wheels. • Dot Matrix Printer (DMP): Uses a vertical matrix of 9 or 24 electromagnetic pins in the print head striking the ink ribbon. Produces carbon duplicate copies, low cost per page, but noisy and low resolution (72-360 DPI). • Daisy Wheel Printer: Wheel with petal characters striking ribbon. Letter-quality text, but cannot print graphics. • Line Printers (Drum/Chain): Prints an entire line of text at once at high speed (300 - 3000 lines/min) for mainframe batch reports. 2. Non-Impact Printers (No Physical Contact with Paper): • Inkjet Printer: Sprays microscopic droplets of liquid ink through thousands of piezoelectric or thermal heating nozzles (bubbles) directly onto paper (Resolution: 600 - 4800 DPI). • Laser Printer (Electrophotographic Mechanism): 1. Charging: Primary corona wire / roller coats the rotating photoconductive selenium drum with uniform negative electrostatic charge. 2. Exposure: A precision Laser Beam discharges specific areas on the drum, drawing an invisible electrostatic latent image. 3. Development: Negatively charged black toner powder clings exclusively to the laser-discharged areas on the drum. 4. Transfer: Paper receives a strong positive charge, pulling toner particles from the drum onto the paper surface. 5. Fusing: Heated fuser rollers melt and press plastic toner particles permanently into paper fibers at ~200°C. 6. Characteristics: Ultra-fast (20 – 60 PPM), crisp 1200+ DPI text, silent, low cost per page for high volume.