Here is another link (from Specialized's site) that goes through all of the types with very well-done
animated diagrams of each type. I
KNEW I'd seen this a while back and forgot where it was. I finally found it:
http://www.specialized.com/sbc4Bar.jsp?a=b
And, yes, it's got a lot of FSR propoganda tilt; but the pictures and descriptions are good references.