If you’re running OS X 10.9 Mavericks, it looks like you’re going to be able to run OS X 10.10 Yosemite.
Per AppleInsider, the following system requirements have been released for the first OS X 10.10 Yosemite beta:
– MacBook Pro: mid-2007 or newer
– MacBook Air: late 2008 or newer
– iMac: mid-2007 or newer
– Mac mini: early 2009 or newer
– Mac Pro: early 2008 or newer
– MacBook: late 2008 aluminum, early 2009 or newer
– Xserve: early 2009
Unfortunately, this fall’s debut of iOS 8 will leave the iPhone 4 in the dust, finally retiring support for Apple’s A4 chip. The oldest phone that will be supported by iOS 8 is the iPhone 4S, which is powered by Apple’s A5 CPU.
Stay tuned for additional details as they become available.