Time marches on and Apple’s never been shy about dropping legacy technology compatibility and the company’s latest, greatest operating system, a.k.a. OS X Mountain Lion, cuts off a huge number recent Macs, many less than three years old — ouch. Get the details here.

OS X 10.6 Snow Leopard dropped support for PowerPC Macs and OS X 10.7 Lion dropped the Rosetta PPC emulation environment, as well as the earliest Core Solo and Core Duo Intel Macs.

With OS X 10.8 Mountain Lion, which is currently available as a developer beta, the cut is Intel’s 950GM and X3100 graphics — Macs running those graphic subsystems aren’t supported. Further, you will need a Mac with a 64-Bit Intel Core 2 Duo processor or better.

Rather than trying to make sense of that, here are separate lists of which Macs will and won’t run OS X Mountain Lion.

Macs that live 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

And, the dead Macs walking:

• Late 2006 iMacs: iMac5,1, iMac5,2, iMac6,1

• All pre-unibody MacBooks (MacBook2,1, MacBook3,1, MacBook4,1)

• MacBook Pros released prior to June 2007 (MacBookPro2,1, MacBookPro2,2)

• Original MacBook Air (MacBookAir1,1)

• Mid-2007 Mac mini (Macmini2,1)

• Original Mac Pro and its 8-core 2007 refresh (MacPro1,1, MacPro2,1)

• Late 2006, early 2008 Xserves (Xserve1,1, Xserve2,1)

I haven’t read anywhere how much RAM you will need, but 2GB seems a reasonable assumption.