Mac OSX Snow Leopard Upgrade: The Facts
Everything you need to know for an easy install
By Ryan Faas | Computerworld US | Published: 12:54, 28 August 2009
In-place upgrade vs. clean install
With a major OS release, there's always the question of whether to perform a simple upgrade (where your files, applications, and system configuration files are left in place) or a clean install (where the target drive is backed up and erased before installation).
In the past, I, like many power users, advocated for a clean install, as it can help avoid conflicts between older applications and the new OS or any damaged configuration files. It can be a good troubleshooting step if you can't find the source of ongoing problems or if you have damaged system files. But the snazzy new installer for Snow Leopard (more on that in a minute) detects potential issues, making a simple in-place upgrade not only sufficient, but the better and easier way to go.
The main advantage to a clean install is from a personal housekeeping perspective. Since most computers over time collect files that are no longer needed - anything from old to-do lists to applications you installed but never use - a clean install forces you to take a look at what's on your computer and do some spring cleaning. Given that it means copying files, erasing the disk, restoring and organizing your files, and resetting all of your preferences and system settings, a full-fledged clean installation isn't worth the hassle. Just find some time to go through your hard drive and clean it out.
If you do perform a clean install, you'll need to boot your computer using the Install DVD by restarting the computer while holding down the C key. Then use Disk Utility (located in the Utilities menu in the menu bar after you've booted from the Install DVD) to select your hard drive and erase it. Quit Disk Utility to return to the installer and proceed with your installation as outlined below. Be forewarned: Starting up from the installation disc and erasing your hard drive for a clean install will make the entire installation process take longer.
Longtime Mac users are probably familiar with the old "Erase and Install" (which erased the contents of the hard drive before installing the new OS) and "Archive and Install" (which retained a copy of all system files for later retrieval) options for installing Mac OS X. Although you can still erase your hard drive for a clean install using the steps outlined above, these two options are no longer part of the actual installation process.
Meet the Mac's new installer
When you put the Snow Leopard Install DVD in your Mac, the Finder window that opens looks pretty much like that of any Mac OS X installation disc (the obvious exception being the Snow Leopard icon).
But the second you double-click the installer, you'll notice something's different. Instead of being asked to restart your Mac and boot from the Install disc, you'll see a screen with two options: Utilities and Continue. That's because you don't need to boot from the DVD to install Snow Leopard (though you can do so later down the road if your Mac has problems or if you want to erase your hard drive before selling your computer, for instance).