Printer is a device used to print text and illustrations created using a computer. There are three main types of printers: (1) laser printers, (2) inkjet printers, and (3) impact printers. Each type of printer responds to instructions from software in the computer.
Laser printers
use a process adapted from photocopying machines. A tiny, precise laser electrically charges portions of a light-sensitive metal drum, duplicating on its surface the text or images created on the computer. Dry ink called toner is oppositely charged and dusted onto the drum. The toner sticks only to the charged parts of the drum. Paper is given an electrical charge matching that on the charged portions of the drum but stronger. The paper is then pressed against the drum, and the toner is attracted to the paper. The paper passes through rollers that heat it for an instant, causing the toner to adhere permanently to the paper.
Laser printers can produce several pages of text per minute. They reproduce complex images and photographs more slowly. Some can produce color output. When special paper is used, some laser printers can approach the print quality standards of traditional printing presses. Laser printers have revolutionized the printing and design industries and made possible desktop publishing (the use of personal computers to design and edit publications).
Inkjet printers
use a high-speed nozzle to spray a jet of ink onto paper in a pattern that matches the text or images created on the computer. See Inkjet printer .
Impact printers
include dot-matrix printers and daisy-wheel printers. Dot-matrix printers use tiny pins to strike an inked ribbon, thus transferring ink to paper. Computer software controls the sequence in which the pins strike the ribbon to form letters, numbers, and images. Daisy-wheel printers use a wheel with letters and other characters on it. Software directs the wheel to rotate to the correct position. A hammer hits the positioned character’s “spoke,” which in turn strikes a ribbon, transferring ink to the paper.
Impact printers are among the earliest types of printers, and they are rarely used today. They are still employed, however, in situations that require impact, such as printing on multiple-sheet forms.
