Another Mac OS release, another moment of truth for those using old Macs. Apple's next OS X release, code-named Mountain Lion, will drop support for some older machines as the company continues to move forward with the iOS-ification of the operating system. The list of supported machines has not been publicly published (yet) by Apple, but a developer source has now passed that list along to TUAW after having downloaded the Mountain Lion developer release.

So which Macs get to stay on the island? According to TUAW's source, Mountain Lion will run on:

iMac (mid 2007 or later)

MacBook (13-inch Aluminum, 2008), (13-inch, Early 2009 or later)

MacBook Pro (13-inch, Mid-2009 or later), (15-inch, 2.4/2.2 GHz), (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)

Anything earlier than those machines will not be able to install OS X 10.8 from the Mac App Store. The list of those getting the axe include the original MacBook Air and all pre-unibody plastic MacBooks, iMacs from 2006, pre-June-2007 MacBook Pros, pre-mid-2007 Mac minis, the original and 2007 Mac Pro, and Xserves from 2006 and 2008. Most of those machines were released early enough that it makes sense for Apple to drop support, but there are plenty of Mac users who like to hold onto old hardware and won't be pleased with the latest restrictions. Are you one of them?