printer, computer output device that reproduces data on paper or another medium. Impact printers use a mechanical hammering device to produce each character. A formed character printer forces metal or plastic characters against an inked ribbon to produce a sharp image on paper; the characters may be on a moving bar, a rapidly rotating chain, a rotatable ball, or wheel spokes. A dot matrix printer uses a matrix of tiny pegs that, when hit from behind against a ribbon, impart a set of dots to form a character on the paper; a wide variety of characters and graphics is created using different dot combinations. Although noisy, impact printers can produce multiple copies of business forms simultaneously using carbon or carbonless techniques.

Nonimpact printers use thermal and electrostatic, rather than mechanical, techniques. Ink-jet printers, including bubble-jet printers, squirt heated ink through a matrix of holes to form characters or images. Laser printers form an image of the output on a selenium-coated drum using laser light that is turned on and off by data from the computer and then transfer the output from the drum using photocopying techniques. Thermal-wax-transfer printers and dye-sublimation printers use heat to transfer color pigment from a ribbon to a special paper to produce photographic-quality color images. Nonimpact printers are quieter than impact printers and produce higher quality output, especially of graphics, but at a greater cost per page. See also laser printer.

laser printer, a computer printer that produces high-resolution output by means of a process that is similar to photocopying. In place of reflected light from an image (as is used in xerography), a laser printer uses data sent from a computer to turn a laser beam on and off rapidly as it scans a charged drum. The drum then attracts toner powder to the areas not exposed to the light. Finally, the toner is fused to paper over a belt by heated rollers. In a write-black printer the laser positively charges the printed areas to attract the toner, which gives better detail than a write-white printer. In a write-white printer, the beam negatively charges the areas not to be printed to repel the toner, which gives a denser image. Faster, quieter, and capable of producing more attractive results than standard printers, laser printers have become an important means of printing business documents since they became more generally available (1984) for personal computers. See also desktop publishing.