Apple has confirmed that Mountain Lion, the upcoming 10.8 version of its Mac OS X operating system, will not support all Mac computers with 64-bit processors. Information found in the golden master of Mountain Lion released to developers indicates that the limitation is due to older graphics hardware in the excluded models.
As detailed on Apple's OS X upgrade page, these are the models that will support Mountain Lion:
- 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)
While Apple has provided no official statement on why models older than those on the supported list will not support Mountain Lion, Andrew Cunningham of Ars Technica posited that the exclusions are due to graphics drivers. Mountain Lion's 64-bit only kernel does not support loading 32-bit kernel extensions, such as the 32-bit graphics drivers on Macs older than the models on the supported list.
Ars Technica guesses that Apple decided it was better to cut off these older models, instead of spending the time and resources to update the drivers for older GPUs. The older Mac models will be stuck with Mac OS 10.7, Lion.
Mountain Lion is rumored to launch at the end of July.