Toner carries the powder think of it as a reservoir but of a dry powder
The drum gets charged by the laser and is what directs the toner to the paper so the drum is the most important part but lasts quite a long time
Drums normally last 4 or 5 toners so somewhere around 10000 pages
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you can reset the drum counter as long as you have no issues with your prints
https://www.youtube.com/watch?v=8NovsDGY5RM