Mountain Lion will support many, but not all, 64-bit Macs
According to Apple’s Mountain Lion upgrade page, these are the oldest Macs that can make the move:
- 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 Mountain Lion is a 64-bit operating system, not all 64-bit capable Macs can run the new OS. The reasoning behind that, Ars Technica speculates, is that the unsupported 64-bit Macs use graphics cards with 32-bit drivers, and those aren’t Mountain Lion compatible.
In other words, Apple is requiring Macs with Intel Core 2, 64-bit processors and video cards that support 64-bit drivers to run Mountain Lion.
Apple plans to ship Mountain Lion some time in July and will offer the OS as an upgrade for OS X Snow Leopard and later for US$19.99 as a download from the Mac App Store.