A computer output device which produces characters or graphics on paper. Many different types exist, and the optimum choice for any given situation depends on the acceptable cost, printing speed, print quality, and operating noise.
A computer printer, or more commonly just a printer, is a device that produces a hard copy (permanent human-readable text and/or graphics) of documents stored in electronic form, usually on physical print media such as paper or transparencies.
Printers are designed for low-volume, short-turnaround print jobs; and many consumer printers are far slower than that), and the cost-per-page is relatively high, In contrast, the printing press (which serves much the same function), is designed and optimized for high-volume print jobs such as newspaper print runs--printing presses are capable of hundreds of pages per minute or more, and have an incremental cost-per-page which is a fraction of that of printers. However, as printers have improved in quality and performance, many jobs which used to be done by professional print shops are now done by users on local printers;
Printing technology
Printers are routinely classified by the underlying print technology they employ; The choice of print engine has a substantial effect on what jobs a printer is suitable for, as different technologies are capable of different levels of image/text quality, print speed, low cost, noise;
Another aspect of printer technology that is often forgotten is resistance to alteration: liquid ink such as from an inkjet head 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.
Modern print technology
The following printing technologies are routinely found in modern printers, as of April 2006:
Toner-based printers
Toner-based printers work using the Xerographic principle that is at work in most photocopiers: by adhering toner to a light-sensitive print drum, then using static electricity to transfer the toner to the printing medium to which it is fused with heat and pressure. Laser printers are known for high quality prints, good print speed, and a low cost-per-copy;
Laser printers are available in both color and monochrome varieties.
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 spray very small, precise amounts (usually a few picolitres) of ink onto the media. Inkjet printing (and the related bubble-jet technology) are the most common consumer print technology; some, known as photo printers, include extra pigments to better reproduce the color gamut needed for high-quality photographic prints (and are additionally capable of printing on photographic card stock, as opposed to plain office paper).
Inkjet printers consist of nozzles that produce very small ink bubbles that turn into tiny droplets of ink. Ink-jet printers can print high quality text and graphics. Inkjet printers have a much lower initial cost than do laser printers, but have a much higher cost-per-copy, as the ink needs to be frequently replaced.
Inkjet printers are also far slower than laser printers.
Solid Ink printers
Solid Ink printers, also known as phase-change printers, are a type of thermal transfer printer.
Solid ink printers are most commonly used as color office printers, and are excellent at printing on transparencies and other non-porous media. Previously, solid ink printers were manufactured by Tektronix, but Tek sold the printing business to Xerox in 2000.
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. While once the province of high-end print shops, dye-sublimation printers are now increasingly used as dedicated consumer photo printers.
Thermal printers
Thermal printers work by selectively heating regions of special heat-sensitive paper. These printers are limited to special-purpose applications such as cash registers and the printers in ATMs and gasoline dispensers.
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. All but the dot matrix printer rely on the use of formed characters, letterforms that represent each of the characters that the printer was capable of printing. In addition, most of these printers were limited to monochrome printing in a single typeface at one time, although bolding and underlining of text could be done by overstriking, that is, printing two or more impressions in the same character position. Impact printers varieties include, Typewriter-derived printers, Teletypewriter-derived printers, Daisy wheel printers, Dot matrix printers and Line printers.
Pen-based plotters were an alternate printing technology once common in engineering and architectural firms.
Only plotters, dot matrix printers, and certain line printers were capable of printing graphics.
Typewriter-derived printers
Several different computer printers were simply computer-controlable versions of existing electric typewriters. The Flexowriter printed with a conventional typebar mechanism while the Selectric used IBM's well-known "golf ball" printing mechanism.
Teletypewriter-derived printers
The common teleprinter could easily be interfaced to the computer and became very popular except for those computers manufactured by IBM.
Daisy wheel printers
Daisy-wheel printers operate in much the same fashion as a typewriter.
These printers were also referred to as letter-quality printers because, during their heyday, they could produce text which was as clear and crisp as a typewriter (though they were nowhere near the quality of printing presses). The fastest letter-quality printers printed at 30 characters per second.
Dot-matrix printers
In the general sense many printers rely on a matrix of pixels, or dots, that together form the larger image. However, the term dot matrix printer is specifically used for impact printers that use a matrix of small pins to create precise dots.
Dot-matrix printers can be broadly divided into two major classes:
Ballistic wire printers (discussed in the dot matrix printers article) Stored energy printersDot matrix printers can either be character-based or line-based (that is, a single horizontal series of pixels across the page), referring to the configuration of the print head.
At one time, dot matrix printers were one of the more common types of printers used for general use - such as for home and small office use. Such printers would have either 9 or 24 pins on the print head. 24 pin print heads were able to print at a higher quality. Once the price of inkjet printers dropped to the point where they were competitive with dot matrix printers, dot matrix printers began to fall out of favor for general use.
Some dot matrix printers, such as the NEC P6300, can be upgraded to print in color. Color graphics are generally printed in four passes at standard resolution, thus slowing down printing considerably.
Dot matrix printers are still commonly used in low-cost, low-quality applications like cash registers, or in demanding, very high volume applications like invoice printing. The fact that they use an impact printing method allows them to be used to print multi-part documents using carbonless copy paper (like sales invoices and credit card receipts), whereas other printing methods are unusable with paper of this type. Dot-matrix printers are now (as of 2005) rapidly being superseded even as receipt printers.
Line printers
Line printers, as the name implies, print an entire line of text at a time. In drum printers, a drum carries the entire character set of the printer repeated in each column that is to be printed. In either case, to print a line, precisely timed hammers strike against the back of the paper at the exact moment that the correct character to be printed is passing in front of the paper. The paper presses forward against a ribbon which then presses against the character form and the impression of the character form is printed onto the paper.
Comb printers represent the third major design. These printers were a hybrid of dot matrix printing and line printing. In these printers, a comb of hammers printed a portion of a row of pixels at one time (for example, every eighth pixel). Because far less motion was involved than in a conventional dot matrix printer, these printers were very fast compared to dot matrix printers and were competitive in speed with formed-character line printers while also being able to print dot-matrix graphics.
Line printers were the fastest of all impact printers and were used for bulk printing in large computer centres.
The legacy of line printers lives on in many computer operating systems, which use the abbreviations "lp", "lpr", or "LPT" to refer to printers.
Pen-based plotters
A plotter is a vector graphics printing device which operates by moving a pen over the surface of paper. Plotters have been (and still are) used in applications such as computer-aided design, though they are being replaced with wide-format conventional printers (which nowadays have sufficient resolution to render high-quality vector graphics using a rasterized print engine).
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 Microsphere (printer) (special paper) Spark printer (supplied for Sinclair ZX81) barcode printer uses heat to print barcodesPrinting mode
The data received by a printer may be:
a string of characters a bitmapped image a vector imageSome printers can process all three types of data, others not. Modern printing technology, such as laser printers and inkjet printers, can adequately reproduce all three.
Today it is common to print everything (even plain text) by sending ready bitmapped images to the printer, because it allows better control over formatting.
Monochrome, color and photo printers
A monochrome printer can only produce an image consisting of one color, usually black.
A photo printer is a color printer that can produce images that mimic the color range (gamut) and resolution of photographic methods of printing.
Printing speed
The speed of early printers was measured in units of characters per second.
Printer job classes
They are collections of printers.
Forensic identification
Similar to forensic identification of typewriters, computer printers and copiers can be traced down by imperfections in their output.
Some high-quality color printers and copiers steganographically embed their identification code into the printed pages, as fine and almost invisible patterns of yellow dots.
User Comments Add a comment…