Printer | Research & Encyclopedia Articles

Printer

A printer is a device that converts computer output into printed text or images on paper or some other medium. A printer is considered a peripheral device, as is any part of a computer other than the central processing unit or its working memory: monitors, printers, disk drives, digital cameras, scanners, and so on.

In 1953 the Remington-Rand company developed the first high-speed printer for use with the UNIVAC computer. Today, laser and inkjet printers are two popular types of printers. The original laser printer was developed in 1978 at the Xerox Palo Alto Research Center when Xerox engineer Gary Starkweather added a laser beam to Xerox copier technology. The Hewlett-Packard Company introduced the first desktop laser printer in 1984, basing their device on technology developed by Canon, Inc. Laser printers quickly became popular due to their high-quality printouts and their relatively low operating expenses. Though the inkjet printer was invented in 1976, it wasn't until 1988, when Hewlett-Packard released its DeskJet inkjet printer, that it become a popular consumer item.

Printers are categorized in several ways. The primary distinction is whether a printer prints by impact or non-impact means.

Impact Printers

Impact printers are older, noisier, and generally produce lower-quality output than non-impact printers. In this method of printing, the printing mechanism physically comes into contact with the paper. Examples include the dot-matrix, line, and daisywheel printers.

A dot-matrix printer places ink on paper using a matrix of small, closely packed needles or pins, like a miniature bed of nails. As this print head repeatedly tracks across the page, different pins are activated at each point and hit an ink ribbon, striking a small portion of the ribbon against the paper. Typically, the dot-matrix print head consists of 24 pins in a 4 x 6 arrangement. Dot-matrix printers are noisy and cannot produce high-quality printout, but they are inexpensive and have many uses. Dot-matrix printers were once a relatively low-cost printing option for many people and businesses, but they have been largely replaced by inkjet printers (described in more detail below).

A line printer is, in most cases, a dot matrix printer. However, instead of printing one character at a time, the line printer prints an entire line at a time using a long, narrow matrix of pins. Line printers are very fast, but still produce low-quality print. They are commonly used in data centers and industrial complexes where large amounts of printed material are required. They tend to be large, fast, expensive, and noisy.

A daisywheel printer, similar to a ball-head typewriter, has characters arranged on the ends of the spokes of a plastic or metal wheel (shaped somewhat like a daisy). The wheel is rotated to select the character to print and then an electrically operated hammer mechanism knocks the selected spoke forward, pressing an ink ribbon against the paper. A daisywheel printer can produce letter-quality print but cannot print graphics. Daisywheel printers were common in the 1980s, but they declined in use when laser and inkjet printers became affordable. Of similar construction, specially designed electronic typewriter keyboards, such as the line of IBM Selectric Typewriters, were connected to computer logic and memory circuits in order to perform automatic functions such as printing multiple copies of a given letter. These devices, too, have fallen out of general use.

Non-impact Printers

Non-impact printers print without striking the paper. They are much quieter than impact printers, are faster due to the absence of moving parts in the print head, and generally produce higher-quality print. Examples include laser, inkjet, LED/LCD, and thermal printers. A laser printer uses a laser beam to form an electrostatic image on a drum (i.e., a pattern of electric charge that corresponds to the image to be printed). This attracts electrically charged dry ink powder (toner) which is then transferred to paper and heat-fused (melted on). Laser printer resolution ranges from 300 to 600 dots per inch (dpi), allowing for increased flexibility of character shapes, which in turn allows the use of TrueType font formats. The highest-quality laser printers, which use chemical photoduplication techniques, can produce resolutions of 2,400 dpi (fine photographic quality). All laser printers produce high-quality text and graphics. An inkjet printer sprays very small ink droplets electrostatically from a nozzle onto a sheet of paper. Charged plates in the ink's path direct the ink stream (broken up into thousands of discrete droplets per second) onto the paper in the desired pattern. Inkjet printers produce high-quality text and graphics, and have become the most popular personal printer technology. An LED printer is one that is similar in operation to a laser printer, but, instead of a laser, an arrangement of light-emitting diodes (LEDs) is used to produce a charge image on the drum. A thermal printer is an inexpensive printer that works by pushing heated pins against heat-sensitive paper. Thermal printers are widely used in printing calculators and in barcode and fax machines.

Methods of categorizing printers include:

• 1. Print technology used (dot-matrix, inkjet, laser, etc.);
• 2. character formation technique used, which may involve either (a) completely formed, solid characters (e.g., laser, daisywheel) or (b) characters composed of patterns of dots (e.g., dot-matrix and inkjet);
• 3. method of transmission from computer to printer, such as (a) byte-by-byte transmission with parallel ports or (b) bit-by-bit transmission with serial ports;
• 4. method of printing, namely (a) character-by-character (e.g., dot-matrix, inkjet), (b) line-by-line (line printers), or (c) page-by-page (laser);
• 5. quality, namely photo quality, letter quality, or draft quality; and
• 6. speed, namely output speed measured in either characters per second (cps) or pages per minute (ppm).

Daisywheel printers are usually the slowest, printing about 30 cps (less than a page per minute), while dot-matrix printers can print up to 500 cps. Laser printers range from about 4 to 20 ppm.

Word processing programs have transformed the processes of typing and editing, contributing dramatic new flexibility to the writing process. Computer printers tracked this process as they moved through several stages of innovation, from the first impact printers (daisywheel and dot-matrix) to the current generation of affordable, high-quality non-impact printers (inkjet and laser).