1. Confirm Hardware Compatibility

A good general rule of thumb with new major versions of OS X has been that they will support Macs made in the last four years. That was largely borne out with Tiger (Mac OS X 10.4), Leopard (Mac OS X 10.5), Snow Leopard (Mac OS X 10.6), and Lion (Mac OS X 10.7), with a few exceptions. Like those operating systems, Mountain Lion, released in late July 2012, supports many (but not every) Mac model made since 2008. Some models apparently didn’t make the cut because their on-board graphics hardware wasn’t up to the demands placed on it by Mountain Lion.

You can tell which Mac you have by two bits of information: its name and its Model Identifier. You can find the latter by holding down the Option key and choosing ...

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