Link Download OS X Yosemite 10.10.5 Pre-Release( Build 14F6a)

Most Macintosh products capable of running OS X Mountain Lion (v10.8.x) are supported by Yosemite; all models capable of running OS X Mavericks(v10.9.x) are able to run Yosemite since they have the same requirements. However, in order to take full advantage of the Handoff feature, additional minimum system requirements include a Mac with Bluetooth LE (Bluetooth 4.0). As with Mavericks and Mountain Lion, 2 GB of RAM, 8 GB of available storage, and OS X 10.6.8 (Snow Leopard) or later are required.

These are the models that are compatible with OS X Yosemite (with exceptions):

• iMac (Mid 2007 or later)
• MacBook (Aluminium Late 2008 and 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)

The Mid 2007 iMac is the first iMac to support seven major OS X versions: 10.4-10.10.
These are the models that support new features such as Handoff, Instant Hotspot as well as AirDrop between Mac computers and iOS devices:

• MacBook Air (Mid 2012 or later)
• MacBook Pro (Mid 2012 or later)
• iMac (Late 2012 or later)
• Mac Mini (Late 2012 or later)
• Mac Pro (Late 2013 or later)