what is printer

what is printer

The printer is the most common output device. It produces permanent visual record of the data output from a computer. It is capable of producing business reports and documents currently available. Printers are capable of printing from 150 to over 20,000 lines per minute, with each line having up to 150 characters. Thus, a maximum printing speeds of approximately 50,000 characters per second is possible.

Printers print on plain paper or on specially prepared single-or multiple copy forms, such as invoices, stationery, labels, checks, bills and other special-purpose forms used in business and industry. They can print both text and graphics in black and white or in color.

Printers can be subdivided into two broad categories, impact and non-impact.

Impact Printers

In impact printers, printing occurs as a result of a hammer striking a character form and the character form in turn striking an inked ribbon, causing the ribbon to press an image of the character on paper.

Character printer devices print one character at a time at speeds of about 10 to 500 characters per second. Thc fastest of these printers is the wire or dot matrix printer. It prints characters made up of a pattern of dots formed by the ends of small wires. By extending certain wires beyond the others, a dot pattern can he created that gives the appearance of numbers, letters or special characters.

These extended wires are pressed against an inked ribbon to print the characters on the paper. Some slower and less expensive matrix printers print a character as a series of columns each one dot wide. It can be used to print special character shapes that can be used with graphics.

For a typewriter-quality output, a special dot matrix or daisy metal print element, similar in appearance to the arrangement of petalson a daisy flower. This element is rotated until the correct character is in position, and then pressed against an inked ribbon. The process as repeated for each character to be printed on a line. Typical for such printers range from 25 to 100 characters per second.

Impact character printers are the common output devices used with personal and small business microcomputer systems. They are significantly cheaper than the line printers. Impact line printers, capable of printing a whole line at a time, employ print wheels or a moving chain or drum. The print-wheel printer consists of print wheels, each containing a full complement of digits and alphabetic characters in addition to a set of special characters. For printing, all print wheels rate positioned to represent the data to be printed on one line. They then impact simultaneously at a speed of about 150 lines per minute. Impact line printers and the chain and drum printers are commonly used. As the print chain or drum revives, each character is printed as it comes into position. Up to 150 characters per line can he printed at speeds of up to 2,500 lines per minute. Impact line printers are used almost exclusively to support larger computer systems.

Non Impact Printers

Non impact line printers using laser, xerographic, electrostatic, or ink jet methods are the fastest printers. Before the development of the ink jet and laser printers, non impact were not heavily used, for several reasons:

# Special and more expensive paper was required.

# Printed output was not as sharp or as clear as with impact printers.

# Only a single-part form can be printed at a time.

# Output could not be easily or satisfactorily copied on office copiers.

Electrostatic and xerographic printers place a pattern of the desired character on sensitized paper by means of an electric current or beam of light. The paper then passes through a powdery black substance called toner, which contains dry ink particles. The ink particles are attracted to the exposed paper and the character becomes visible. These printers can print at speeds of from 3500 to 20,000 lines per minute.

The laser printer form characters by projecting a laser beam of dot matrix pattern on a drum surface. Toner is then attracted to the area exposed by the laser and transferred to the paper. The paper is then passed over a heating element, which melts the toner to form a permanent character.

Many types of ink jet printers are available. The simplest of these contains a series of ink jet nozzles in the form of a matrix. Vibrating crystals force ink droplets, roughly the diameter of a human hair, from selected nozzles to form an image in the same manner as an image is formed by a matrix printer. Different colored inks may be used and combined to form additional colors. Several hundred nozzles are employed in the more sophisticated ink jet printers to direct a continuous stream of droplets across the page to form an image. These charged ink droplets travel at speeds of up to 40 miles per hour as they move between a set of plates that deflect the droplets. Droplets not needed are attracted away by electrostatic charge from the paper for reuse. A stream of more than 100,000 droplets can form approximately 200 characters per second.

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