Here are a list of devices which will run Mountain lion:
- iMac (mid 2007 or later)
- MacBook (13-inch Aluminum, 2008), (13-inch, Early 2009 or later)
- MacBook Pro (13-inch, Mid-2009 or later), (15-inch, 2.4/2.2 GHz), (17-inch, Late 2007 or later)
- (Late 2008 or later)
- Mac Mini (Early 2009 or later)
- Mac Pro (Early 2008 or later)
- Xserve (Early 2009)
All the macbooks (before they became macbook airs) won't be compatible. iMacs made before 2007 will also go. To find out what device your mac is, go to Apple symbol > About this mac > System report > Hardware overview. The 'model identifier' will show you the exact type of mac.
For more infomation, click here: http://www.ijailbreak.com/news/os-x-mountain-lion-system-requirements/
Hope this was a help!