Wow, they must have made improved the efficiency a lot over Windows 7, where the official minimum hardware specs were a joke.
Which machine? The following are all compatible with Yosemite:
- 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)
So Apple is still supporting machines five, six or seven years old with the very latest OS, depending on model.