A noob question about CPU usage on Lion.

If you have two cores, it's capable of 100% for each, for a total of 200%.

 

Not entirely sure what you're asking, but the processor usage is not measured from 0-100%. Each processor in modern Macs has a virtual core for each physical core, so a dual-core processor will present itself to the system as having four core, each of which can be 100% utilized, so at any given time, you could see up to 400% processor utilization. On a quad-core Mac, it's double that even. The high end Mac Pro can actually have 2400% processor utilization if you manage to max it out. This is the source of most of the confusion I've seen from other about this type of thing, so hopefully it's helpful.

EDIT: Heh, I was too slow. I'll work on this question now though:

Many applications can't use multiple processor cores, so it's normal that they might max out one while the other remains idle.

jW