There is no space on the motherboard. The Mini 9 runs hot like most netbooks but there is no internal fan. I've had my system board replaced twice in one month. First time the card reader died, the second time the SSD burned, literally burned. A note from the tech engineer who repaired it stated that I shouldn't run the Mini 9 plugged in for longer than two or three hours due to the overheating issue, even less if running wi-fi. As a third-party repair outfit contracted by Dell (Flextronics) he's dealt with a number of overheated Mini 9s and filed reports with Dell.
Needless to say I returned the thing disappointed.