A printer is an external hardware output device that takes electronic data stored on a computer or other device and generates a hard copy (physical printout) on paper or transparency film.
Broad Classification of Printers
- Impact Printers: Mechanically strike an inked ribbon against paper (e.g., Dot Matrix, Line Printers).
- Non-Impact Printers: Print without physically striking the paper using heat, ink spray, or static electricity (e.g., Inkjet, Laser Printers).
1. Dot Matrix Printer (DMP)
A Dot Matrix Printer is a character impact printer that forms images and characters by striking tiny pins against an inked ribbon onto paper.
Figure 1: Dot Matrix Impact Printer
Working Principle:
The print head contains a vertical array of pins (typically 9 pins or 24 pins). Solenoids fire these pins selectively to form a matrix of dots (e.g., 5x7 or 7x9 grid) that form letters or symbols.
- Very low per-page printing cost.
- Can produce multipart carbon copies (due to physical impact).
- Works with continuous tractor-feed paper.
- Extremely noisy operation.
- Low printing speed (measured in CPS: Characters Per Second).
- Poor print resolution and color capabilities.
2. Line Printer
A Line Printer is a high-speed impact printer that prints an entire line of text at once rather than character by character. Common types include Drum Printers and Chain/Band Printers.
Working Principle:
In a drum or chain mechanism, characters rotate at high speed behind the paper. A series of hammers hit the paper against the rotating characters through an inked ribbon at the exact millisecond the desired character lines up.
- Extremely high speed (measured in LPM: Lines Per Minute, up to 3000 LPM).
- Heavy-duty reliability for bulk printing.
- Handles carbon copies effectively.
- Cannot print graphics or photos.
- Very large physical size and high noise levels.
- Fixed font styles based on physical characters.
3. Inkjet Printer
An Inkjet Printer is a non-impact printer that creates images by spraying fine microscopic droplets of liquid ink onto paper.
Figure 2: Color Inkjet Desktop Printer
Working Principle:
Utilizes liquid ink cartridges or ink tanks (CMYK: Cyan, Magenta, Yellow, Black). Thermal or Piezoelectric nozzles heat or vibrate to propel precise liquid ink droplets onto paper, creating high-detail images.
- High-quality color photo printing.
- Low upfront hardware cost.
- Quiet and compact operation.
- Higher running cost per page (liquid ink).
- Print nozzles can clog if left unused for long periods.
- Water-sensitive output on standard paper.
4. Laser Printer
A Laser Printer is a non-impact page printer that uses a laser beam, electrostatics, and powdered toner to produce sharp text and high-resolution graphics rapidly.
Figure 3: Office Laser Printer
Working Principle:
- Charging: A primary corona wire or roller charges an OPC (Organic Photoconductor) drum.
- Exposing: A laser beam writes an electrostatic image onto the drum.
- Developing: Dry powdered toner clings to the charged regions of the drum.
- Transferring & Fusing: Toner is transferred to paper, and heated rollers (fuser unit) melt the toner permanently onto the paper fibers.
- Exceptional speed (measured in PPM: Pages Per Minute).
- Crisp, smudge-proof text printing.
- Low cost per page for monochrome printing.
- Higher initial printer purchase price.
- Toner cartridges and fuser replacements are expensive.
Printer Comparison Table
| Feature | Dot Matrix | Line Printer | Inkjet Printer | Laser Printer |
|---|---|---|---|---|
| Category | Impact (Character) | Impact (Line) | Non-Impact (Page) | Non-Impact (Page) |
| Consumable | Inked Ribbon | Inked Ribbon | Liquid Ink Cartridge | Dry Powder Toner |
| Speed Unit | CPS (Char/Sec) | LPM (Lines/Min) | PPM (Pages/Min) | PPM (Pages/Min) |
| Primary Application | Billing, Invoices | Data Centers, Payroll | Home, Photo Printing | Offices, High Volume |
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