July 28, 2012, 7:17 AM — [Editors note: This article is part of our series of articles on installing and upgrading to Mountain Lion.]
It used to be that when upgrading to a major new version of OS X, installing over an existing OS X installation -- for example, installing 10.3 over 10.2 -- entailed some degree of risk, as existing applications, add-ons, and support files could conflict with the new OS. For this reason, many people used to perform a clean install: wiping your hard drive (after backing it up, of course), installing the latest version of OS X, and then either using Setup/Migration Assistant to restore your applications and data, or manually copying over your data and reinstalling programs. (The Mac OS X 10.2 installer actually included an Archive And Install option, which preserved your original OS in a special folder while installing a completely new, fresh copy of 10.3. This feature was eliminated in the Snow Leopard OS X 10.6 installer.)
But a new download-and-install procedure debuted with Lion (OS X 10.7) and continues with Mountain Lion (OS X 10.8) -- instead of a bootable installation DVD, you download the latest OS X installer to your Mac and install it from the same drive. As with Lion last year, many Mac users are asking two related questions: (1) Can you perform a clean install of Mountain Lion? and (2) Should you? Heres my take on each of these questions.
Can you perform a clean install of Mountain Lion?
First, the technical question: Given that the OS X 10.8 installer doesnt include an official clean-install option, is it possible to perform such an installation? The simple answer is: Yes. As explained in my main article on installing Mountain Lion, the installer will let you install the new OS onto a blank drive. So if you first back up your existing Snow Leopard or Lion installation and all your filesI recommend creating a bootable clone using SuperDuper or Carbon Copy Cloneryou can then boot from a bootable installer drive, erase your Macs normal startup drive, and install Mountain Lion on it. In fact, you can use the instructions in my article on how to install Mountain Lion over Leopard. Specifically, scroll down to the section called The brute-force method and perform Steps 1 through 7, substituting Snow Leopard or Lion for Leopardthe result is a clean install.