Well my Colour laser printer has four cartridges , also known as CYMK ( cyan - yellow - magenta - and black )
It also has an imaging drum .
The imaging drum reads each page you put through the printer . However , if you only print 1/3 of a page , it will be read as a full page .
So you will get a message to say that your imaging drum is empty after a certain number of pages - say 5,000 ) even though it is not empty.
So by buying a reset chip on eBay , I can continue to use the imaging drum for a long long time extra .
BTW , an imaging drum for my HP cost around € 180 and a reset chip cost about € 15
I hope this makes sense .