Although OS X and OS 9 are completely different operating systems under the hood, Apple has tried to make OS X's interface as similar to OS 9's as possible while still being able to add functionality and make it look "new and improved." So if you're making the transition from OS 9, after a few hours of working in X you'll most likely be doing quite well. However, a few issues tend to be very confusing, both for users and for applications.
Documents folders Unless you used OS 9's Multiple Users feature (few people actually did), all of your Documents were stored in a folder called Documents at the root level of your hard drive. As described in Chapter 1, OS X uses a different Documents folder for each user, found inside /Users/username.
Unfortunately, many Classic applications (those written for OS 9) that require or access files in your Documents folder have problems with this location change. For example, as I explained in Chapter 9, if you have "Use preferences from home folder" checked in Classic preferences, the Classic Environment tells all Classic applications to use the Documents folder inside your user folder. If you haven't yet moved documents from the root level of your hard drive to your private user folder, Classic applications won't be able to find them. Conversely, if you don't have this option checked, Classic applications will look for documents in a folder at the root level of your hard drive (more specifically, the root level of the hard drive hosting your Classic System Folder). This presents a problem if you've moved your files into private user folder(s).
For these reasons, it's important to make sure that your Classic preferences and your Documents are set up congruently. I recommend moving documents to the appropriate user folder and then enabling the "Use preferences from home folder" option. (If you're the only user of your Mac, you can also place an alias to your personal Documents folder at the root level of your hard drive, and rename it Desktop Folder, so that Classic applications will always be able to locate documents.)
File comments In both OS 9 and OS X, if you use the Finder's Get Info command on a file or folder, you can enter your own comments or notes about that item. However, for some reason that is beyond my comprehension, Apple decided that OS X shouldn't recognize OS 9 file comments (at least from the very first versions of OS X to the time of this writing). The comments still exist; it's just that OS X can't read them. Likewise, any comments you add in OS X will exist when booted into OS 9, but OS 9 can't read them.
Fortunately, a few third-party software solutions allow you to keep your comments when transitioning to OS X. The freeware Comment Converter and the shareware File Buddy (both from http://www.skytag.com/) will import your OS 9 file/folder comments into OS X. In the case of Comment Converter, you simply drag files and folders onto the application's icon, and it automatically transfers comments for you. (File Buddy will also do this, but because it's a multifunction utility, it takes a couple more steps.)
In addition, if you tend to boot into OS 9 and OS X, the shareware Comment Synch (http://preciousgem.dnsalias.com:90/preciousgem/index.html) will actually synchronize comments both ways—so that you can also view your OS X file comments in OS 9. (It also makes adding and editing comments easier by allowing you to do so within its own file browser, so you don't have to use the Finder's Get Info command.)
Translated file names OS X uses the standard Unicode character encoding for naming files, and for displaying those filenames. However, OS 9 uses proprietary character sets created/provided by Apple. If you save, copy, or rename a file on an HFS Plus (a.k.a., Mac OS Extended) volume while booted into OS 9, OS 9 automatically converts its filename to Unicode so that it will also work under OS X.
Unfortunately, when you later boot into OS X, sometimes you'll find that these converted filenames contain odd characters or weren't translated properly. This is most likely to happen when the OS 9 encoding used for a filename differs from the primary language of your OS 9 installation (for example, when you use an Asian-language character set on an English version of OS 9.)
If you experience this problem, Apple provides the File Name Encoding Repair Utility, which runs under OS X, that fixes these encoding problems. You simply drop a file, or a folder of files, onto the utility, select the correct encoding from the resulting dialog, and click Repair. For more information on this utility, and/or to download it, visit http://docs.info.apple.com/article.html?artnum=86182.