Upgrade Mac OS X
The default method, Upgrade Mac OS X, attempts to make the transition as simple as possible by leaving all your files, applications, and settings in place. The installer replaces all the components of your old Mac OS X installation with their Tiger equivalents, and deletes those that are obsolete. Meanwhile, it leaves all user-installed files (including preferences) intact.
Sounds great, doesn’t it? In theory it is, but this approach can lead to serious problems. Most importantly, some of the third-party software you have installed may conflict with Tiger. When you restart after installing Tiger, if a serious conflict exists, you may experience a system-wide crash known as a kernel panic , application crashes, indecipherable error messages, or other malfunctions. Other customizations you may have applied to your old operating system, such as command-line hacks, can also cause problems for Tiger. Even a disk error that never showed itself under Panther can manifest itself after a default upgrade.
To be fair, not every user is at risk for problems with this sort of upgrade. If you’ve never installed any non-Apple software or modified your system beyond documented preferences, your chances of problems are low. This is especially true if you have a very new Mac, or if you performed a clean installation of Panther recently.
The more modifications you’ve made, and the longer you’ve gone since a major operating system installation or upgrade, the greater the risk of problems with this method.
Archive and Install
Starting with Jaguar, Apple introduced an upgrade method called Archive and Install. This is similar to the Clean Install method available in Mac OS 9, but more advanced. Archive and Install creates a completely new, clean system but maintains a copy of your old system files so you can manually copy over any important items after the new operating system is up and running.
Archive and Install includes an option called Preserve Users and Network Settings. If you select this (and you should), Archive and Install leaves your home folder(s) (the contents of the /Users folder) in place, so that documents, preferences, and network settings for all user accounts are maintained after the upgrade.
Note: The Tiger installer claims that if you select Preserve Users and Network Settings, you will skip Setup Assistant when installation is complete. This isn’t quite true: it does run, but in an abbreviated form—it asks only for your Apple ID and registration information, and doesn’t take up the whole screen as it does normally.
Archive and Install avoids most compatibility problems because the installer does not copy the contents of your old System folder (including third-party extensions and login items) to the new system; it also skips several other folders inside /Library and at the root level of your disk. Although Archive and Install is not foolproof, it’s much more reliable than the default method, Upgrade Mac OS X.
The downside to Archive and Install is that this method requires some manual effort afterward to locate and copy the extra files you need. In some cases—particularly if you have a lot of third-party utilities, fonts, and other software—this can be a huge and frustrating amount of manual effort. Archive and Install also requires a significant amount of free disk space, because it must maintain an extra copy of many old files. But the reward for your efforts will be a cleaner, more stable system and a far smaller likelihood of having to do time-consuming troubleshooting.
Archive and Install should be available as an option both in the full version of the Tiger Install DVD and in the upgrade DVD available through the Mac OS X Up-to-Date program.
Erase and Install
For a perfectly clean, pristine installation of Tiger, you can choose Erase and Install, which all but guarantees a fully operational system when the installation finishes. Unlike the other two installation methods, it wipes out any hidden directory corruption, file system problems, or other disk gremlins that may cause problems.
Of course, there’s a price to pay for a perfect system: all your preferences, network settings, user-installed software, and documents will be gone, and you must either restore them from a backup or recreate them from scratch. Depending on how many changes you’ve made to your system, this may be a daunting task.
That’s where Apple’s new file transfer feature (a.k.a. “migration technology”) comes in. Immediately after an Erase and Install, Setup Assistant runs automatically and offers to copy all your personal files from another volume (or even another Mac). If you’ve made a bootable backup onto an external hard disk or another partition on your internal drive, the installer will do 90 percent of the copying work for you. (And the other 10 percent? See the Restore Missing Files section at the end of this excerpt.) Erase and Install also requires much less disk space than Archive and Install.
Erase and Install is ideal for users with an external hard drive (or two) that can be used for backup. It is also the best method if your hard disk has errors that Disk Utility is unable to repair or if you’re simply paranoid and want to avoid any chance of problems.
Note: Erase and Install erases only the volume you select. It will not affect partitioning or wipe out the contents of other partitions.
File Transfer Vs. Archive and Install
If you were to compare two systems side-by-side—one upgraded using Archive and Install, and the other using Erase and Install (with all options selected on the File Transfer screen)—you would find that Erase and Install transfers many more files and folders to the active system. If you use Archive and Install, you’ll have to transfer all the rest manually. To avoid that effort, I recommend using Erase and Install, along with the File Transfer feature, if possible.