[Mark Dobson] "I just think it's important to start moving forward especially with the news that Mountain Lion will not run on some older 64-Bit Macs."
The root of the 10.8 cutoff seems to be
old GPU drivers that run on 32-bit kernel extensions, or "kexts". Mountain Lion is the first OS X version to drop support for 32-bit kexts, so there is no way for the graphics cards in those older otherwise 64-bit Macs to work. But the Mac Pro is also the only Mac you can swap GPUs on, so while a
stock 2006 Mac Pro with its factory GPU might not run MoLo, a 2006 Mac Pro with a Radeon 5770 might, since it would be loading the 64-bit kexts for that card upon booting.
A Retina MBP would still outrun it though.
Best,
Andy
