The biggest physical difference is the mounting system, as you might be able to see Noctua has changed it up a little (it's now even easier to install then the original). With the NH-U9B you get mounting brackets for the LGA775, LGA1336, LGA1156 from Intel, and the AM, AM2, AM2+ sockets from AMD which should pretty much cover the good majority of CPU's produced in the past few years. . .



Link: BCC Hardware