Instead of using a bootable installation DVD, you download the latest OS X installer to your Mac and install the new OS from the same drive. This feature was eliminated in the Snow Leopard OS X 10.6 installer.)īut a new download-and-install procedure debuted with Lion (OS X 10.7) and has continued through Mavericks (OS X 10.9). (The Mac OS X 10.2 installer debuted an Archive And Install option, which preserved your original 10.1-or problematic 10.2-installation in a special folder while installing a completely new, fresh copy of Mac OS X 10.2. For this reason, many people performed 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 reinstalling programs and copying over your data. It used to be that if you upgraded 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.