One of the most important parts of a laser printer is the laser printer drum unit.  This is the main part of the laser printer, as it allows for the printing process to take place on the paper.  Through this mechanism, paper is printed efficiently and cheaply.  The laser printer drum unit resembles a drum and hence it gets its name from its shape.

The laser printer drum contains an electrically charged wire that discharges a positive charge to the drum.  Thus since the drum is charged, it acts as a photoreceptor.  The laser part of the laser printer burns the image of the printed document on the drum.  Thus, an electrostatic image is formed on the drum; then the drum is coated with toner or positively charged black ink.  Hence, the laser writes on the photoconductive drum, as the ink goes toward the negatively charged parts of the paper.

As you can see, the laser printer drum is the most important part of the printer.  Although, a toner may last between 1000 to 5000 pages; the drum can last for over a 100,000 pages.  In the initial models of laser printers, the drum was not separate from the toner and you had to change the drum unit frequently.  Nowadays, with proper care, the laser printer drum will last for many toners with proper care. 

One of the things that you have to watch out for is the fact that you should not use your toner to the end.  When the toner is about to finish, the drum will be coated with less ink then usual and thus this can cause the photoreceptor surface to get damaged.  In addition, most manufacturers suggest that you turn off your laser printer when you are not using it, so that the drum will not remain charged all the time.