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OS X Mountain Lion Officially Drops Support for Some Older 64-Bit Macs
Your Mac must be one of the following models:Ars Technica has more on Apple's decision, including discussion of why Apple has dropped support for some early 64-bit Macs that do support OS X 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)
Apple declined to tell us the reasoning behind leaving some of these models out of potential Mountain Lion upgrades, but we suspected it was related to an updated graphics architecture that was designed to improve OS X's graphics subsystem going forward. Our own Andrew Cunningham suspected the issue was related to graphics drivers, since the GPUs not supported under Mountain Lion had drivers that were written before 64-bit support was common.The report notes that some of the GPUs used in early 64-bit Macs were deprecated before 64-bit KEXTs were in common usage, and thus they were never upgraded from their original 32-bit KEXTs. With the affected machines now being a number of years old, Apple apparently decided that it was not worth investing the resources to upgrade those drivers to 64-bit in order to support OS X Mountain Lion.
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 no longer supports loading 32-bit kernel extensions (KEXTs).