While I never took the cooler apart (it seems to be fastened well in place and I don't feel like breaking anything just yet), the rear reveals the 10 internal fins. Although pretty small (this would be an equivalent to a 40mm fan), the one ACS uses is incredibly powerful yet quiet. The breeze coming out the exhaust holes is very noticeable and even during stress tests, barely warm. Which brings up another point: because of the ACS orientation, at least half the memory chips (those on the front that is) will get some active cooling if you attach ramsinks with fins. This is due to the air being directed that way.