by Dinesh Thakur

Until now you may have not seriously considered using a printer. After all, if you do not use your personal computer to play or to calculate your family budget you do not really need a hard copy of what is displayed on the screen.

But when you begin to work more effectively with your personal computer, the constraints imposed by the fact of not having printer will become more obvious. If you write your own programs, you may want to keep a copy of your listings. If you use your computer to do your accounting, a printed copy of the calculations will be necessary.

There are three types of printers for personal computers: dot matrix printers, printers, daisy and thermal printers.

A Dot Matrix Printer or Impact Matrix Printer refers to a type of computer printer with a print head that runs back and forth on the page and prints by impact, striking an ink-soaked cloth ribbon against the paper, much like a typewriter. Unlike a typewriter or daisy wheel printer, letters are drawn out of a dot matrix, and thus, varied fonts and arbitrary graphics can be produced.

 Because the printing involves mechanical pressure, these printers can create carbon copies and carbonless copies. Each dot is produced by a tiny metal rod, also called a "wire" or "pin", which is driven forward by the power of a tiny electromagnet or solenoid, either directly or through small levers (pawls). Facing the ribbon and the paper is a small guide plate pierced with holes to serve as guides for the pins. The moving portion of the printer is called the print head, and when running the printer as a generic text device it generally prints one line of text at a time.

Most dot matrix printers have a single vertical line of dotmaking equipment on their print heads; others have a few interleaved rows in order to improve dot density. These machines can be highly durable, but eventually wear out. Ink invades the guide plate of the print head, causing grit to adhere to it; this grit slowly causes the channels in the guide plate to wear from circles into ovals or slots, providing less and less accurate guidance to the printing wires.

Dot-matrix printers are two important characteristics : 

Speed : Given in characters per second (cps), the speed can vary from about 50 to over 500 cps. Most dot-matrix printers offer differen speeds depending on the quality of print desired.

Print Quality : Determined by the number of pins (the mechanisms that print the dots), it can vary from 9 to 24. The best dot-matrix printers (24 pins) can produce near letter-quality type, although you can still see a difference if you look closely.

Advantages :

1. can print on multi-part stationery or make carbon copies.

2. Impact printers have one of the lowest printing costs per page.

3. They are able to use continuous paper rather than requiring individual sheets.

4. The ink ribbon also does not easily dry out.

Disadvantages :

1. Impact printers are usually noisy.

2. They can only print low resolution graphics, with limited colour performance, limited quality and comparatively low speed.

3. They are prone to bent pins (and therefore a destroyed printhead) caused by printing a character half-on and half-off the label.