Some 64-Bit Macs May Not Work With Mountain Lion Due To Graphics Cards

Posted Jul 11, 2012

Apple has confirmed that Mountain Lion has some limitations on certain 64-bit Mac models and it will extend to the final release.  This means that certain 64-bit capable MacBook Pros, iMacs, and Mac Pros will be restricted from upgrading to Mountain Lion when it goes public later this month.  The limitation appears to be caused by the graphics cards built into the devices.  Lion is 64-bit and can run on any Core 2 or newer 64-bit Intel processor.

Mountain Lion is compatible with any Mac that is capable of running a 64-bit kernel, but the kernel does not support loading 32-bit kernel extensions (KEXTs) as of right now.  Macs that have older EFI versions that are not 64-bit clean will not load Mountain Lion’s 64-bit only kernel.  Below is a list of Macs that are supported by Mountain Lion as put together by Ars Technica:

iMac (Mid 2007 or newer)
MacBook (Late 2008 Aluminum, or Early 2009 or newer)
MacBook Pro (Mid/Late 2007 or newer)
MacBook Air (Late 2008 or newer)
Mac mini (Early 2009 or newer)
Mac Pro (Early 2008 or newer)
Xserve (Early 2009)