Printer: There are two types of printers impact and non-impact printers. Printers are used to produce hard copy. 

Impact Printers: There is a mechanical contact between print head and the paper. 

1. Dot Matrix Printer: Here characters are formed by using dots. The printing head contains a vertical array of pins. The letters are formed by using 5 dot rows and 7 dot columns. Such a pattern is called 5 × 7 matrix. 

This head moves across the paper, the selected pins fire against an inked ribbon to form characters by dot. They are capable of faster printing, but their quality is not good.

2. Non-impact Printers: 

There is no mechanical contact between print head and paper so carbon copies cannot be possible to take. They are inkjet, laser, thermal printers etc.

(a) Inkjet Printer: 

It works in the same fashion as dot matrix printers, but the dots are formed with tiny droplets of ink to be fired from a bottle through a nozzle. These droplets are deflected by an electric field using horizontal and vertical deflection plates to form characters and images.

It is possible to generate colour output. They produce less noise and produce high quality printing output. The printing cost is higher. Here liquid ink is used. 

(b) Laser Printer: 

It uses photo copying technology. Here instead of liquid ink dry ink powder called toner is used. A drum coated with positively charged photo conductive material is scanned by a laser beam. The positive charges that are illuminated by the beam are dissipated. The drum is then rolled through a reservoir of negatively charged toner which is picked up by the charged portions of the drum.

It adheres to the positive charges and hence creating a page image on the drum. Monochrome laser printer uses a single toner whereas the colour, laser printer uses four toners. Its print quality is good less noise and printing cost is higher.

(c) Thermal Printers: 

It is same as dot matrix printer but it needs heat sensitive paper. It produces images by pushing electrically heated pins to the special paper. It does not make an impact on the paper so we cannot produce carbon copies. It produce less noise, low quality print and inexpensive. It is used in fax machine.

3. Plotter: 

A plotter is a device that draws pictures or diagrams on paper based on commands from a computer. Plotters draw lines using a pen. Pen plotters generally use drum or flat bed paper holders. In a drum plotter the paper is mounted on the surface of a drum. 

Here the paper is rotated. But in a flatbed plotter the paper does not move and the pen holding mechanism provides the motion that draws pictures. Plotters are used in engineering applications where precision is needed.

4. Three Dimensional (3D) printer: 

This device is used to print 3D objects.