Right after Tiger shipped, two and a half years ago, I wrote an article here about my impressions of the upgrade procedure (see "Evaluating the Tiger Installation Process," 2005-05-02). I began by saying that the installer was much better than its predecessor, so much so that I might not be able to sell as many ebooks about upgrading as I had when Panther was released! Nevertheless, I found enough surprises that I could say, with all sincerity, that the average Mac user is likely to have an easier and more successful upgrading experience with a bit of expert guidance.
Well, today I'd like to sing another verse of the same song. Yet again, Apple has made substantial improvements to the installer, and in general, the Leopard installation is easier and more reliable than the Tiger installation was. Also, yet again, some aspects of the upgrade process can cause unexpected problems. Based on the feedback I've received from readers of "Take Control of Upgrading to Leopard," the many additional pages of advice and instructions I added about preparing your Mac to run Leopard - and solving problems before, during, and after upgrading - have been more than worthwhile.
System Requirements -- Apple always increases the minimum threshold for hardware compatibility when they release a major upgrade to Mac OS X. But most people assumed Leopard would run on any Mac with a G4 or better processor. Not so: if you have a G4-based Mac, it must be faster than 867 MHz. A question I've heard numerous times is, "What about my dual-800 MHz Power Mac? Isn't that faster than 867 MHz?" The answer, as far as the Leopard installer is concerned, is no. It doesn't matter if your computer is almost fast enough, or if it has multiple processors, each of which is almost fast enough. If the installer doesn't see an 867 MHz or faster processor, it won't let you install. I have heard of some hacks that could let some users of older Macs run Leopard, but I can't recommend them because Apple won't have tested Leopard on those machines, so you may encounter other problems, such as video card incompatibilities and software update failures.
Installation Methods -- Apple has made some improvements to the Archive and Install upgrade method. Specifically, it copies many more folders and files from your old /Library folder to your new one, meaning you'll have less work to do afterward to restore everything to its proper place. The net result is that if you use Archive and Install, with the Preserve Users and Network Settings option selected, you'll get virtually the same result as if you use Erase and Install along with the option of transferring old files from a backup drive at the end. I still think Erase and Install is better, because even if the sets of files you end up with are the same with either method, Erase and Install can wipe out lots of random disk gremlins, as well as reducing disk fragmentation (for what that's worth).
Most people, of course (at least those who don't read my book) will stick with the default Upgrade method. It works reasonably well - in fact, it seems to be more robust than the same method in Tiger. However, as ever, it isn't smart enough to disable all of the innumerable doohickeys you may have installed that could conflict with Leopard. I've read reports, for example, of old versions of Unsanity's Application Enhancer causing blue screen hangs after an Upgrade installation; a variety of other system add-ons, especially those that hack Mac OS X in ways Apple officially discourages, could also cause problems. As long as you have a fresh, bootable duplicate, though, you risk little by trying the Upgrade method - except the expense of time to redo the installation if it fails. Speaking of which...
Make a Backup -- Do not under any circumstances even consider thinking about upgrading to Leopard without a complete, recent, and verified backup of your drive, preferably a bootable duplicate. (Two backups would be even better.) You should do this not only in case something goes wrong during the upgrade itself, but so that you can go back to your previous system, later, if you find out in a few days or a week that something simply isn't working for you in Leopard. Even for people who have no trouble with Leopard at all, a bootable duplicate is extremely helpful in that it lets you use the Erase and Install method without losing any of your old data or applications.
AirPort in the Installer -- For reasons I can't comprehend, when you're running the Leopard installer from the DVD, the AirPort status icon appears in the menu bar. Initially it indicates that AirPort is off, but you can turn it back on and join a wireless network right there, in the installer. I can't think of any reason why you'd want or need to do this, Apple doesn't mention it in their documentation, and I've read several reports of people having difficulties with the installation process after attempting to join a wireless network while booted from the DVD. Why would Apple include this seemingly useless feature, which can only tempt people to take an unnecessary action that might actually cause problems?
Differently Disabled -- When I wrote about the Tiger installer, I complained that it didn't automatically disable login items on the disk you're upgrading, an obvious source of potential conflicts. The Leopard installer has the same problem, regardless of which upgrade method you choose. On the other hand, it may in some situations disable certain software (such as Now Up-to-Date & Contact) without giving any explanation of why it did that, or what components specifically were affected.
Boot Camp Drivers -- Now that Boot Camp is officially part of Mac OS X, Apple includes the latest version of their Boot Camp Windows Drivers on the Leopard DVD itself. So if you're using Boot Camp, you should reboot in Windows right after installing Leopard, reinsert your Leopard DVD, and let the installer run to update your Apple drivers to the latest version.
You Can Take Control -- The Leopard installer isn't bad; it's definitely an improvement over the Tiger installer, and nicer even than the much-improved installer Microsoft offers for Windows Vista. Nevertheless - and I'm speaking as someone who has installed Leopard dozens of times, using many different options, on several machines - that "just-run-it-and-it-works" experience that Apple wants you to believe in may or may not be a reality. If you have a relatively clean system, it could be just that simple. But the more modifications you've made under Tiger or Panther, the greater your chances of glitches when upgrading. And, even the most scrupulous Mac user could fall victim to random disk errors or other unforeseen problems. So although upgrading to Leopard is not difficult, and is not something you should fear or avoid - not even in the initial, 10.5.0 release - make sure you do it right. For detailed guidance in getting your Mac ready for Leopard, performing that crucial full backup, choosing an upgrade method, and working through problems you could encounter in the process, read "Take Control of Upgrading to Leopard," a 125-page ebook that spells out everything you need to know to make the transition as smooth as possible.