what a 'drum unit' is
Hello, Could you tell me what a 'drum unit' is, compared to a toner cartridge please?
The drum unit is an aluminum cylinder coated with photosensitive material that clips onto the back of
the toner. Drum unit is a consumable part need to replace after every 4-5 toners, when your prints appear excessively blackened, or you get a check drum warning.
The drum unit does not come with a toner, so you need to buy the toner separately.
Normally, for replacing the drum, you need to remove the drum kit which including the drum and the toner from the printer. place your workfull toner back to the newly drum unit. then place the drum kit back to the printer.
Either single drum or toner would not make your printer work.
You can also refer to below link for how to replace drum: