Opteron 100 200 800 series

what's the difference between the 175 / 275 / 875 opteron processors? Is it that you can run only 1 of them with the 175 on a mobo, and you can run 2 275's on a dual mobo, and up to 8 875's on an 8-way board?
I just want to make sure..because most of us workstation users would only need the 175, as it performs the same as the 275/875 just you can only run one of them on a motherboard?

Or am I totally messed up here?

well simple answer, the 1XX can only run in single. 2XX can run in single but can also run in double (not sure about the single part though, I know it can run in double) and the 8XX can run in 8 ways (I guess it could run double and single). There is no point to run a 1XX personally because the reason you get SMP for the multitasking, which needs more than once cpu.

Yep you got it right.
1xx = 1 way
2xx = 2 way
8xx = 4/8 way