The work of a printer is to leave a legible permanent impression on a sheet of paper. Different printers have different ways of doing this. But a LaserJet printer does this via having ink stored in a powdery form stored in a toner cartridge deposited on the sheet of paper with the assistance of a drum unit and laser.
To go into more details, the toner cartridge contains a fine polyester powder which is capable of being electrically charged and attracted to an opposite charge. The required opposite charge is created on a photosensitive electric drum (also known as printer drum) by a laser. Then the toner cartridge deposits polyester powder on the outline formed on the charged printer drum. The printing paper is then charged as it passes through the printer, and with the aid of a hot fuser, attracts and appends the polyester particles from the printer drum to itself forming smudge-free prints.
This process makes it possible to have very fast print speeds. But also leads to higher cost for a LaserJet printer compared to an Inkjet printer.
Furthermore, LaserJet printer users need to be aware that some laser printers have their drums and toners built in together as a single unit while others have their drums and toners built separately. Knowing this distinction is important. As it affects if you need to replace the toners simultaneously with the printer drum or if you can separately replace either the toner or the printer drum. Both of these alternatives have cost implications.
But currently, a good rule of thumb to follow is to know that modern laser printers from manufacturers such as HP usually come with imaging drum built in with the toner. Other manufacturers such as Brother, have laser printers that have printer drum and the toner built separately. But Brother also has laser printers that have the imaging drum built in with the toner. To aid your search on which printer uses which, I recommend you use the toner cartridge finder on 123ink.ca to identify the specification of printer drum/toner specification to use for a brand of printer.