Output Device : Printers

A printer is a peripheral which produces a text and/or graphics of documents stored in electronic form, usually on physical print media such as paper or transparencies. Many printers are primarily used as local peripherals, and are attached by a printer cable or, in most newer printers, a USB cable to a computer which serves as a document source.
Some printers, commonly known as network printers, have built-in network interfaces, typically wireless and/or Ethernet based, and can serve as a hard copy device for any user on the network. Individual printers are often designed to support both local and network connected users at the same time.
In addition, a few modern printers can directly interface to electronic media such as memory cards, or to image capture devices such as digital cameras, scanners; some printers are combined with a scanners and/or fax machines in a single unit, and can function as photocopiers. Printers that include non-printing features are sometimes called multifunction printers (MFP), multi-function devices (MFD), or all-in-one (AIO) printers. Most MFPs include printing, scanning, and copying among their many features.
Impact Printers:
These printers use the electromechanical mechanism, that is pressing a typeface against an inked ribbon, Which marks it on a paper and prints the characters. Egs: DMP (Dot Matrix Printer), Drum and Daisy-Wheel printer. Impact printers can further be divided into two types:
   a) Line Printers which print one line at a time eg. drum and chain printers whereas
   b) Character printers print one character at a time.
Drum Printer: It has a rapidly rotating cylindrical drum on which characters are embossed in a standard 132-column printer. There are 132 bands containing every possible character.
There are 132 hammers lifting the paper-and -ribbon drums. Logic circulating in the printer makes a hammer(which is electromagnetically operated) strike against the drum as the required character to be printed passes through. Likewise, the sequence continues and a line is printed on the paper.
Chain Printers: The mechanism of printing is slightly different as in a drum printer. The drum rotates vertically in circular motion and there is a set of characters for every hammer. In a chain printer, the chain is the unit on which letters are embossed and it moves horizontally in a circular motion against the hammers. The mechanism of hammers striking against the chain is almost similar. A chain consists of five or six sets of characters. whenever a character which is required to be printed passes in front of the hammer position, the hammer strikes and the character impression gets printed on the paper. the paper and ribbon both move in between the chain and hammer.
Character Printers:
They print a character at a time. Examples are the dot matrix printer and the Daisy Wheel printer.
Dot-Matrix Printer:
Unlike the drum and chain printer which have letters embossed with the hammer striking against it, dot-matrix printers generally have seven or nine impact pins. these pins fire or strike under the control of a printer logic through an electromagnetic motion. the complete unit comprises of impact pins and coils - called the printer head.
The paper on which the printing is done moves up and down depending upon the model of the printer. The printer head moves left to right or vice-versa, permitting a 5x7 - matrix character for a 7-pin head and a 7x9 matrix character for a 9-pin head. The speed of the dot matrix printers is noted in CPS (characters per second). These printers come in widths of 80 columns and 132 columns.
Daisy-wheel Printers:
This is a character with a daisy wheel on which characters are embossed. There is a hammer against the wheel. the paper movement is similar to the dot-matrix printer. The presence of one hammer ensures that one character is printed at a time in Daisy-Wheel printer.

Non-Impact Printers
These printers do not use an electro-mechanical printing head to strike against ribbon and paper. They use thermal, chemical, electrostatic, laser beam or inkjet technology for printing. Examples are thermal, inkjet and laser printers. these printers are faster than the impact printers.

Inkjet Printers:
They print characters by spraying small drops of ink onto paper. A special ink with high iron content is used. the droplets of ink are charged electrically after being lead onto a nozzle. The droplets are then guided to thin proper positions on paper by electrically-charged deflection plates. These are high-quality printers and are therefore better than impact printers.
Laser Printers
Laser printers use light beams to form images on paper using a toner ink as a medium. A beam of light strikes the exposed parts of the drum surface. The light beam gets electrically charged and exposed areas attract the toner ink particles. The toner particles are then deposited on and permanently fixed to the paper using heat or pressure. Laser printers are quiet workers. they produce very high-quality output both textually and graphically.
Thermal Printers
These printers use heat to make a mark on heat-sensitive paper. the print head contains needles which are pressed against the paper. On applying heat to the selected pins, the paper changes colour to form a pattern of dots.

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