NBC 101 • Unit 216 min read★ Very High Exam Frequency

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

Q: Why are Dot Matrix Printers still used at Railway Ticket counters and Banks despite being noisy and slow?

Dot Matrix printers are Impact printers that use physical mechanical pressure to strike through multi-ply carbon paper, creating simultaneous duplicate receipts in a single pass at an extraordinarily low cost per page. (Examiner Tip: Laser and Inkjet printers cannot produce carbon duplicate copies because they do not physically press the paper.)

Unit 2: Computer Memory Hierarchy, Storage & I/O Systems • Fundamentals of Computer

👨‍🏫 Professor's Mental Model: The Painter's Canvas vs The High-Speed Press

Output devices computer ke dimaag ke results ko human-readable banate hain. Monitor screen digital canvas jaisa hai jo millions of red-green-blue pixels ko glow karta hai. Aur Printers computer ke paper press hain: Dot Matrix printer purane typewriter jaisa hammer maar kar awaz karta hai (Impact), jabki Laser Printer ultra-sharp laser light aur static electricity se powder toner pighla kar 1 second me poora page print kar deta hai (Non-Impact)!

Academic Lecture Notes & Solved Study Pages

Unit 2 • Core Concepts, Step-by-Step Proofs & Notebook Solutions

2 Notebook Pages

NOTEBOOK PAGE 1 OF 2• Lecture Study Sheet

1. Display Technologies Architecture

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).

NOTEBOOK PAGE 2 OF 2• Lecture Study Sheet

2. Printer Classification: Impact vs Non-Impact Printers

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.

Master Impact vs Non-Impact Printers Comparative Table

Parameter	Impact Printers (Dot Matrix)	Non-Impact Printers (Laser / Inkjet)
Printing Method	Physical mechanical hammer strike on ink ribbon	Laser electrostatics / Ink droplet spray (No strike)
Print Speed	Measured in CPS / LPM (Slow to Medium)	Measured in PPM (Pages Per Minute: 20 - 60+ PPM)
Resolution / Quality	Low resolution (72 - 360 DPI, visible dots)	High to Ultra-High resolution (600 - 4800 DPI)
Noise Level	Noisy mechanical clatter	Virtually silent operation
Carbon Copy Ability	YES (Produces multiple carbon copies via pressure)	NO (Cannot produce carbon pressure copies)
Consumables	Fabric inked ribbon cartridge	Toner powder cartridge (Laser) / Liquid ink (Inkjet)
Typical Applications	Railway ticketing, Bank passbooks, Billing invoices	Office documentation, Book publishing, Photo printing

🎯 University Exam Scoring Blueprint

Explain the 5-stage working mechanism of a Laser Printer (Charging, Exposure, Development, Transfer, Fusing).
Draw a 7-parameter comparison table between Impact and Non-Impact printers.
Define DPI (Dots Per Inch) and PPM (Pages Per Minute).