Here's a List of Macs Compatible With OS X Yosemite
As with every major release of OS X, some Mac can not be updated. For OS X 10.10 Yosemite, all Mac already running on Moutains Lions and Mavericks will be able to move to the new version. The reasons are simple, the basics of Yosemite are the same, only a few cosmetic changes and the addition of new features have been introduced. It is possible, however, that we should add a little more RAM to the system to be more fluid.
iMac (Mid-2007 or later)
MacBook (13-inch Aluminum, Late 2008), (13-inch, Early 2009 or later)
MacBook Pro (13-inch, Mid-2009 or later), (15-inch, Mid/Late 2007 or later), (17-inch, Late 2007 or later)
MacBook Air (Late 2008 or later)
Mac Mini (Early 2009 or later)
Mac Pro (Early 2008 or later)
Xserve (Early 2009)
This is the second year running that a new OS X version has supported the same Macs as its predecessor, following three releases that all dumped a handful of Macs. 10.6 dropped all PowerPC Macs, 10.7 dropped support for all Macs with 32-bit Intel processors, and 10.8 dropped support for all Macs without 64-bit EFI firmware and 64-bit graphics drivers.
