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In computing, a printer is a peripheral which produces a text 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 new printers, a USB cable to a computer which serves as a documents source. Some printers, commonly known as networks printers, have built-in network interfaces, typically wireless 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.

Modern Printer

Printing technology
Printers are routinely classified by the printer technology they employ; numerous such technologies have been developed over the years. The choice of engine has a substantial effect on what jobs a printer is suitable for, as different technologies are capable of different levels of image or text quality, print speed, cost, and noise. Some printer technologies don’t work with certain types of physical media, such as carbon paper or transparencies.
A second aspect of printer technology that is often forgotten is resistance to alteration; liquid ink, such as from an inkjet lead or fabric ribbon, becomes absorbed by the paper fibers, so documents printed with liquid ink are more difficult to alter than documents printed with toner or solid inks, which do not penetrate below the paper surface.
Cheques should either be printed with liquid ink or on special cheque paper with toner anchorage. For similar reasons carbon film ribbons for IBM Electric typewriters bore labels warning against using them to type negotiable instrument such as cheques. The machine readable lower portion of a cheque, however, must be printed using MICR toner or ink. Banks and other clearing houses employ automation equipment that relies on the magnetic flux from these specially printed characters to function properly.

Modern Print Technology
The following printing technologies are routinely found in modern printers:

Toner-based printers
A laser printer rapidly produces high quality text and graphics. As with digital photocopiers and multifunction printers (MFPs), laser printers employ a xerographic printing process but differ from analog photocopiers in that the image is produced by the direct scanning of a laser beam across the printer’s photo receptor.
Another toner-based printer is the LED printer which uses an array of LEDs instead of a laser to cause toner adhesion to the print drum.

Liquid inkjet printers
Inkjet printers operate by propelling variably-sized droplets of liquid ink onto almost any sized page. They are the most common type of computer printer used by consumers. Today’s photo-quality ink jet printers can typically with a resolution of 1200 to 4800 dots per inch. They will give acceptable quality photo prints of images with 140-200 pixels per inch (PPI) resolution, and high quality prints of images with 200-300 p pi resolution.

Solid ink printers
Solid ink printers, also known as phase-change printer, are a type of thermal transfer printer. They use solid sticks of CMYK- clouted ink, similar in consistency to candle wax, which are melted and fed into a pies crystal operated print-head. The print-head sprays the ink on a rotating, oil coated drum. The paper then passes over the print drum, at which time the image is immediately transferred, or transfixed, to the page. Solid ink printers are most commonly used as color office printers, and are excellent at printing on transparencies and other non-porous media.

Dye sublimation Printers
A dye-sublimation printer (or dye-sub printer) is a printer which employs a printing process that uses heat to transfer dye to a medium such as a plastic card, paper or canvas. The process is usually to lay one colour at a time using a ribbon that has colour panels. Dye sub printers are intended primarily for high quality colour applications, including colour photography; and are less well-suited for text.

Inkless printers

Thermal printers
 Thermal printers work by selectively heating regions of special heat-sensitive paper. Monochrome thermal printers are used in cash registers, ATMs, gasoline dispensers and some older inexpensive fax machines. Colours can be achieved with special papers and different temperatures and heating rates for different colours; these coloured sheets are not required in black-and-white output. One example is the ZINK technology.

UV printers
Xerox is working on an inkless printer which will use a special reusable paper coated with a few micrometers of UV light sensitive chemicals. The printer will use a special UV light bar which will be able to write and crease the paper. As of early 2007 this technology is still in development and the text on the printed pages can only last between 16-24 hours before fading.

Obsolete and special-purpose printing technologies

The following technologies are either obsolete, or limited to special applications though most were, at one time, in widespread use.
·       Impact printers
·       Typewriter-derived printers
·       Teletypewriter-derived printers
·       Daisy wheel printers
·       Dot-matrix printers
·       Line printers
·       Liquid ink electrostatic printers
·       Pen-based plotters

Other printers
A number of other sorts of printers are important for historical reasons, or for special purpose uses:
·       Digital minilab (photographic paper)
·       Electrolytic printers
·       Spark printers
·       Barcode printer multiple technologies, including: thermal printing, inkjet printing, and laser printing barcodes.
·       Billboard / sign paint spray printers
·       Laser etching (product packaging) industrial printers
·       Microsphere (special paper)

Printing Mode
The data received by a printer may be:
o   A string of characters
o   A bitmapped image
o   A vector image

Some printers can process all three types of data, others not.
Character printers, such as daisy wheel printers, can handle only plain text data or rather simple point plots.
Pen plotters typically process vector images. Inkjet bared plotters can adequately reproduce all three.
Modern printing technology, such as laser printers and inkjet printers, can adequately reproduce all three. This is especially true of printers equipped with support for Postscript or PCL, which includes the vast majority of printers produced today.

Today it is common to printing everything (even plain text) by sending ready bitmapped images to the printer, because it allows better control over formatting. Many printer drivers do not use the text mode at all, even if the printer is capable of it.