Early adopters of Mac products, prepare to get the shaft. Per Ars Technica, Apple has released system requirements for machines eligible OS X Mountain Lion upgrades and has revealed that pre-2007 iMacs, pre-2008 Mac Pros, MacBook Airs released in the first half of 2008 and MacBook Pros released before mid-2007 haven’t made the cut.

Ars writes that while “Apple declined to tell us the reasoning behind leaving some of these models,” the publication speculates that “it was related to an updated graphics architecture that was designed to improve OS X’s graphics subsystem going forward,” such as when Apple released a MacBook Air with an upgraded GPU in October 2008, 10 months after the laptop line’s initial unveiling.

Apple has posted a complete how-to guide on its website for anyone with an eligible computer who wants to upgrade to OS X Mountain Lion.

Read [Apple] Read [Ars Technica]