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Unformatted text preview: lthough printers capable of
printing in a single or two to three colors are suitable for producing textual documents, it
is often desirable to have printers, which can print in multiple colors for producing
multiple-color graphics outputs. According to this classification, printers are classified as
monochrome printers and color printers.
The various types of printers in use today are described below.
Dot-matrix printers are character printers that form characters and all kinds of images as a
pattern of dots. Figure 9.24 shows how various types of characters can be formed as a
pattern of dots. Based on this idea, the printing mechanism used by dot-matrix printers is
illustrated in Figure 9.25. As shown in the figure, a dot-matrix printer has a print head
that can move horizontally (left to right and right to left) across the paper. The print head
contains an array of pins, which can be activated independent of each other to extend and
strike against an inked ribbon to form a pattern of dots on the paper. To print a character,
the printer activates the appropriate set of pins as the print head moves horizontally. For
faster printing, many dot matrix printers are designed to print both while the print head
moves from left to right and while it moves from right to left on return. A dot-matrix
printer is shown in Figure 9.26. In Figure 9.24 all the characters are formed by 5 horizontal and 7 vertical dots. Such a
pattern is called a 5 x 7 matrix. It can be generated by a print head having 7 pins.
However, you will notice that the print head in Figure 9.25 has 9 pins. The bottom 2 pins
are used for lower-case letters that extend below the line (for example, p, g, q and y).
The quality of the printed output is directly proportional to the density of the dots in the
matrix. Most early dot matrix printers had 9 pins and used 5 x 7 dot matrix patterns for
character formation. So the character that they printed had a maximum vertical resolution
of 7 dots. Many new dot matrix printers have 18 or 24 pins, which can print near-letterquality characters that appea...
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This document was uploaded on 04/07/2014.
- Spring '14