In the last four weeks, Apple has focused on readying a series of new or enhanced features in its desktop operating system, ranging from the entirely new Game Center to tweaks such as the move of Notes from Mail into a standalone app of its own, mirroring how notes are handled on iOS.
Apple warns that some features in the new DP2 build, referred to as 4F134, such as Screen Sharing, have changed enough during development to make VNC remote screen sharing sessions currently incompatible with earlier versions of OS X.
A variety of other OS X Mountain Lion features have been enhanced or built upon, including support for 64-bit software.
The new version of OS X now requires a 64-bit kernel, something that will require kernel extensions (including many device drivers) to support 64-bit operation.
The new release will also be restricted to running on machines that support running a 64-bit kernel, including, minimally:
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)