A laser printer has many components that make up the technology system used to quickly generate documents that meet a professional standard. The rollers pull the paper through and the toner actually makes the images and lettering visible to the human eye, but it is the imaging drum that is the central piece in these highly advanced printers. Also referred to as a drum unit and a photoreceptor assembly, the imaging drum is ultimately responsible for the transfer of printer toner and image or text to the paper.

Initially, the drum receives a positive charge from the corona wire. The laser then writes on the drum, leaving a negative charge in the shape of the image or text that is being printed. The toner is attracted to this charge and clings to the imaging drum where the negative charge is. The rollers are then used to pull the paper through the machine, and the negative charge of the paper is stronger than that of the drum. As a result, the toner is pulled from the drum to the paper, creating a precise document in an efficient matter of time.

Most printers have separate slots for the drum and toner cartridge to be installed in to. Other units, like Brother printers require a drum and a Brother toner cartridge, but the two snap together and are installed into the printer as one assembly. Some printers have toner cartridges that the drum is built into the cartridge and are replaced as one consumable. Be sure to understand which system your machine uses so you can be sure to purchase the right kind of replacements.

For visual effect, here is the difference between imaging drums and drum assemblies:

Imaging Drum	Imaging Drum Assembly (with toner cartridge)

Don't feel bad if you are having trouble identifying which is the cartridge and which is the drum. Just remember, the imaging drum will always have a long roller, typically green. It is important not to touch the surface of the roller or expose it to intense light, as it is sensitive.

Being blasted with lasers frequently can take its toll on an imaging drum. The wear and tear will start to build up, and the quality will suffer as a result. Standard text documents will begin printing with dark spots or even lines across the printed pages. Images that are printed will start to look lighter, even with a brand new toner cartridge installed. It wouldn't hurt to run the printer's internal cleaning system and printing a test page before determining that the issue is indeed the imaging drum.