Printer and Scanner

Printer:

Printer is a device that prints text or illustrations on paper. There are many different types of printers. In terms of the technology utilized, printers fall into the following categories:

Types of printer:

daisy-wheel: Similar to a ball-head typewriter, this type of printer has a plastic or metal wheel on which the shape of each character stands out in relief. A hammer presses the wheel against a ribbon, which in turn makes an ink stain in the shape of the character on the paper.Daisy-wheel printers produce letter-quality print but cannot print graphics.

dot-matrix: Creates characters by striking pins against an ink ribbon. Each pin makes a dot, and combinations of dots form characters and illustrations.

ink-jet: Sprays ink at a sheet of paper. Ink-jet printers produce high-quality text and graphics.

laser: Uses the same technology as copy machines. Laser printers produce very high quality text and graphics.

LCD & LED : Similar to a laser printer, but uses liquid crystals or light-emitting diodes rather than a laser to produce an image on the drum.

line printer: Contains a chain of characters or pins that print an entire line at one time. Line printers are very fast, but produce low-quality print.

thermal printer: An inexpensive printer that works by pushing heated pins against heat-sensitive paper. Thermal printers are widely used in calculators and fax machines.

Scanner:

Scanner is a device that can read text or illustrations printed on paper and translate the information into a form the computer can use. A scanner works by digitizing an image -- dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in. (For color and gray scaling, the same principle applies, but each box is then represented by up to 24 bits.) The resulting matrix of bits, called a bit map, can then be stored in a file, displayed on a screen, and manipulated by programs.

Optical scanners do not distinguish text from illustrations; they represent all images as bit maps. Therefore, you cannot directly edit text that has been scanned. To edit text read by an optical scanner, you need an optical character recognition (OCR ) system to translate the image into ASCII characters. Most optical scanners sold today come with OCR packages.