Meaning behind the B T E and r on the Dell Systems?

I'm trying to sort out which system I want to get~ but am being confused by all these letters!

I thought that maybe the "b" was for the faster bus, and maybe the "E" was coppermine...I want a COPPERMINE chip for starts... and have a Dimension T750r saved in a cart...is this a coppermine chip, or what?

Answers to these questions will be greatly appreciated!

Thanks much~