Apple generally is a company that likes to look forward more than back, and in recent years this has led to an ever-shortening gap between buying a new Mac and watching it become unsupported by the newest OS release, particularly as the company has gone to a yearly refresh cycle for OS X. In something of a surprise move, however, Apple has (at least thus far) made OS X Mavericks (10.9)'s system requirements all but identical to those of Mountain Lion -- meaning Macs as old as mid-2007 may be able to run it.
