Brother MFC-8220 Toner/Drum Question?

Hello


I have a MFC-8220 and the toner needs to be replaced. A few questions





TN-570 - Is the toner part number


DR-510 - Is a ';Drum Unit';


**What is the difference between the two?


**Do I replace both?


A drum unit says it prints 20,000 pages and a toner prints 6,700 pages





I PRINT ALOT! Everytime that I've finished a toner I've just gotten a new one...but what is this ';drum unit';?Brother MFC-8220 Toner/Drum Question?
Drum unit and toner in HP printers are all combined into one - it is more expensive





Brother printer has cheaper running cost because you need to buy 3 toner before you replace the drum kit





Toner containts those black powder that laser printer print on paper





Drum is expensive. Years ago I paid $200 to replace the drum unit





Now you can buy a printer for $200Brother MFC-8220 Toner/Drum Question?
I think the drum unit is the fax mich. part.