How to Install (or Reinstall) OS X
In theory, you should have to install Mountain Lion only once, or never if your Mac came with Mountain Lion preinstalled. And in a perfect world, that would be the case. But you might find occasions when you have to install/reinstall it, such as
If you get a Mac that didn’t come with OS X Mountain Lion preinstalled
If you have a catastrophic hard-drive crash that requires you to initialize (format) or replace your boot drive
If you buy an external hard drive and want it to be capable of being your Mac’s startup disk (that is, a bootable disk)
If you replace your internal hard drive with a larger, faster, or solid state drive
If any essential OS X files become damaged or corrupted, or are deleted or renamed
The following instructions do double duty: They’re what you do to install OS X for the first time on a Mac, and they’re also what you do if something ...
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