You don't want to take those applications you haven't launched in months, giant log files, superfluous startup items, and even old documents you don't need anymore into Snow Leopard, so the first thing you want to do is give your Mac the virtual hose-down. Audit your data, applications, and login items; run some maintenance, and give the old hard drive a checkup with Disk Utility. Here are detailed instructions on how to clean up and revive your bloated, sluggish Mac.
Before You Upgrade, Part 2: Back Up Your Data
Before you crack open that pretty Snow Leopard box, get yourself an external FireWire drive and run a full backup of all the important files on your Mac. If you've got Leopard now you should already be running Time Machine, so make sure you've got a fresh new backup completed. If you're still on Tiger, here are a gaggle of free Mac backup utilities for you to use. (But seriously, if you don't already: get a FireWire drive. Back up your Mac. Now.)
Before You Upgrade, Part 3 (The Extra-Paranoid Track): Make a Bootable Backup of Your Mac
Maybe you go through the entire Snow Leopard upgrade process only to realize that your one, essential, company VPN application isn't yet compatible. Maybe you accidentally lose files or apps in the upgrade process, or you just decide you hate Snow Leopard and want to go back to Leopard stat. One great way to ensure you can go right back to your working Mac's state before an upgrade is to mirror the current state of your Mac on a bootable external hard drive. Even if you've got a Time Machine backup, grab another external drive and clone your Mac's internal hard drive. With a bootable clone on hand, if anything goes wrong or you just want to boot back up into your old Mac's environment (settings, apps, data, and all), you can do so by holding down the T key Option key, restarting your Mac, and choosing the clone as your bootup disk.
The important thing to know is that you can only install the $29 upgrade on top of an existing Leopard installation. That is, you can't start with a formatted Mac hard drive and install Snow Leopard only, which is kind of a bummer for geeks who like to do totally fresh, from-scratch installations.
Correction and update: We have confirmed that the preview of Snow Leopard DOES offer a standalone installer that works on a freshly-formatted hard drive without an existing Leopard installation or DVD. While we can't absolutely say before Friday whether or not the final release will work this way, it's very possible it will. (Read: The full version of the new Mac OS X may be just $29.) My apologies for the mistake! Thanks to commenters RudolphDer and dark42 for asking!
Choose one of two methods for the upgrade.
Upgrade Method 1. Install Snow Leopard Directly on Top of Your Existing Leopard Setup (Easy)
If you're already running a relatively clean installation of Leopard, and you want to make this update as easy, fast, and painless as possible, you're just going to pop your Snow Leopard DVD into your Mac's drive and go. I did this using the Dev Preview of Snow Leopard on a well-used and cluttered Mac, and things went just fine. This is the upgrade path Apple wants you to take and suits most folks—with a good backup, you've nothing to fear. The only possible disadvantage to this approach is that some old logs and system files you don't need might stick around.
Upgrade Method 2. Wipe Your Mac Clean and Start from Scratch (Advanced)
Serious nerds who want their Snow Leopard installation absolutely pristine (and come from the Windows school of wipe-and-reinstall) can go all-out and format their Mac's hard drive, reinstall Leopard, upgrade to Snow Leopard,, install Snow Leopard and then restore their data from backup and reinstall all their essential apps.
The one advantage to this approach is that you can take the opportunity to repartition your Mac's hard drive in the process (though if it's Boot Camp you want, you can set that up any time, not just when wiping your drive). You'll also know for sure your Mac is completely cruft-free. The disadvantage to this approach is that it's tedious and time-consuming. The Snow Leopard installation can take 45 minutes to an hour, then you've got to restore your Time Machine backup (depending on how much data we're talking, this can also take up to an hour) and then you've got to reinstall your applications.
If you do decide to go this route on Snow Leopard upgrade day, here are a few notes:
Only start once you have your Leopard DVD and Snow Leopard DVD in hand, and your data backed up.
Inventory your Mac's application list. Command-line lovers can do a simple ls /Applications/ >> appsiuse.txt to get a textual listing of everything in the Applications folder. Otherwise you can just eye your Applications folder and note down its contents. Also check your System Preferences panes for any panels you've installed there.
After you've inventoried your applications and backed up your data, insert your Leopard DVD and click on "Install Mac OS X."
Insert your Snow Leopard DVD and click on "Install Mac OS X." When you reach the Snow Leopard Installer's "Welcome" screen, from the Utilities menu, choose "Disk Utility..." From there you can (say a little prayer) and format or repartition your Mac's internal hard drive. Once that's done, continue with the installation as usual.
You get a few opportunities to restore your Time Machine backup during the Snow Leopard installation. Even if you pass each time, once Snow Leopard is completely installed, you can get your data out of Time Machine by running the Migration Assistant (located in /Applications/Utilities/).
One important thing to know about restoring a Time Machine backup: you can't be logged in as the same user name that you're restoring. That is, if I'm logged in as gina, and my backed-up Time Machine user is also gina, the Migration Assistant either makes you rename the restored user or log in as another (admin) user to do the restore. The Migration Assistant also lets you decide what you restore: which data (in predetermined folders/categories, like Music, Pictures, Documents, etc), all of your Applications (or none), settings, and other files. Here's what that looks like:
How are you planning to upgrade to Snow Leopard? Are you doing any special Mac prep beforehand? Tell us about it in the comments.
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