The printer is one of the output devices of the computer, which is used to print the results of the computer processing on the relevant media. There are three indicators to measure the quality of a printer: printing resolution, printing speed and noise. There are many types of printers. According to whether the printing element strikes the paper or not, there are impact printers and non-impact printers. According to the structure of printing characters, it is divided into full-width character printer and dot matrix character printer. According to the way that a line of characters are formed on paper, it is divided into a serial printer and a line printer. According to the technology used, it is divided into cylindrical, spherical, inkjet, thermal, laser, electrostatic, magnetic, light-emitting diode and other printers.