Ars Technica notes that Apple has officially confirmed dropping support for certain 64-bit Macs, with its upcoming OS X release, Mountain Lion.
OS X Mountain Lion is set to be publicly released sometime this month for $19.99.
On the “How to upgrade to OS X Mountain Lion” page, under the compatibilty section Apple notes:
Your Mac must be one of the following models:
- 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)
Ars Technica suspects the incompatibility to be due to broken graphics drivers:
[T]he issue is more specifically related to graphics drivers, since the GPUs not supported under Mountain Lion have drivers that were written before 64-bit support was common.
Information included with the first Mountain Lion GM now corroborates the connection to 32-bit graphics drivers as the culprit. While Mountain Lion is compatible with any Mac capable of running a 64-bit kernel, the kernel does not support loading 32-bit kernel extensions (KEXTs). Furthermore, Macs with older EFI versions that are not 64-bit clean won’t load Mountain Lion’s 64-bit only kernel.
Graphic drivers for the now-unsupported Macs were written as 32-bit KEXTs, which aren’t compatible with Mountain Lion.
A Golden Master build of OS X Mountain Lion was seeded to developers earlier this week, indicating that the final release is right around the corner.