What is the difference between a toner cartridge and a drum unit? A toner cartridge is the container that holds the toner powder. The drum unit DR630 is the electrically charged cylinder that transfers that toner powder to paper to create text and images. Brother toner cartridges and drum units DR 630 are sold separately. The toner cartridge usually needs to be replaced first, while the drum unit generally should be replaced after the use of 3 or 4 toner cartridges. The toner clicks into the drum and the two consumables install into the printer together as one piece