With each version of OS X prior to 10.6, the installer DVD presented you with an array of option for installing your new OS. The default option; standard upgrade was the most commonly used, but two other options were archive and install and the dreaded erase and install. Snow Leopard has collapsed this down to one option: install (actuall just the old upgrade option). Why? And does this matter? And if it does matter what can we do?
The old upgrade option was never really the best way to install a new OS, just the easiest. It simply replaced redundant files with newer versions. Leaving large parts of your OS untouched. Great for speed, great for retaining settings but bad if your system was a bit fuzzy round the edges since any corrupted files or other cruft was carried over.
So, the better option was archive and install. This quietly moved your old system to one side and wrote a full new one. Then your settings were moved back into the new system. The best of both worlds, a whole new system plus your network settings etc still in place. The installer even left you with a handy folder labelled "previous system" just in case. Sweet.
However option three, nuke and pave (or archive and install) was also there, ready to spoil the party. Erase and Install, wiped your entire hard drive, before installing your new system. everything brand new, no old settings, no old cruft, but… no old data either. More than one Mac owner has accidentally selected this option, and lost every file they have. You can hear the screams from miles away. When using erase and install, backing up your data is a vital part of the operation.
Partially to prevent this but also because Apple is big on knowing the best way for you to do anything on your Mac, the Snow Leopard installer just gets on with the job. However, you can force an Erase and Install. BUt there is some work to do first. Namely BACK UP YOUR DATA. The easiest way to do this is via Time Machine, just force a backup to commence and once done you have a full recent backup. Alternatively you can make a clone of your hard drive to an external drive using Super Duper or Carbon Copy Cloner (both available for free for this task).
Now you are backed up.
Restarting from your DVD, after selecting English as your main language, instead of proceeding, wait for the menu bar to appear along the top. Now, selecting Disk Utility from the Utilities menu you can select and erase your disk. Your old system AND all your data is gone. Now proceed with an install. After it completes and your Mac restarts, you will be asked to restore your data from either your Time Machine drive or another volume on your Mac (your cloned external drive).
At the end of all this you will have a shiny new OS with all your data back in place, however you will need to re input your network passwords etc as these are not transferred.
Apple have made a big play of how smart the Snow Leopard installer now is, making archive and install redundant, however for some the standard install remains a poor option. At least another option is available even if it's not quite as straightforward as it used to be.
Please note, as mentioned an erase and install will delete ALL data from your hard drive. Dr Happy Mac cannot be held responsible for data loss due to inadequate backup or drive failure during this process. Your data, is your data.
