I keep on reading myths about Mac OS 9, and I'd like to dispell a few here. Some terms that are important here:
Boot into Mac OS 9: If you can switch to Mac OS from Apple menu -> System Preferences -> Startup Disk, select the Mac OS 9 system folder and select restart to get into 9, you can boot into 9. This article tells you the first Macs of each model that can only boot Mac OS X and use Classic:
http://support.apple.com/specs/ will help you identify your Mac.
Classic: If you can start Mac OS 9 from Apple menu -> System Preferences -> Classic, you have Classic. Classic is limited in its support of Mac OS 9 drivers and plugins over booting into Mac OS 9. This means if you have something which requires access to drivers only available in 9 for printers, graphics cards, etc... you may have trouble using it in Classic. Finding drivers for Mac OS X assures better compatibility.
PowerPC versus Intel Macs: Macs released 2006 and later are all Intel Macs. Some hold outs from 2005 were sold in 2006 until they were changed to Intel versions. Go to Apple menu -> About This Mac in Mac OS X to determine if you have an Intel or some form of PowerPC G3, G4, or G5 processor. The G5 is NOT an Intel! Intel Macs can't use Mac OS 9 or Classic. While a hack exists to use 9 on Intel Macs, its reliability and legality is questionable, as the ROM needs to be hacked from a PowerPC Mac to make use of it. These models are obviously Intel by their name:
Mac Pro, MacBook, MacBook Pro
This model can be externally examined to see if it is PowerPC or Intel:
Mac Mini with 2 USB ports is PowerPC, and with 4 USB ports is Intel.
The iMac you have to check the label on its base to find out if it is PowerPC or Intel if you can't boot an operating system on it. This article tells the difference for the iMac:
1. If I upgrade the software on my Mac, Classic or Mac OS 9 will disappear.
2. If I erase and install I won't be able to install 9 or Classic again.
3. Mac OS 9 is included with the retail Mac OS X installation CDs.
4. Upgrading to Mac OS X means my documents created in 9 are no longer usable.
1. Through Mac OS X 10.4.11 (10.4.10 and 10.4.9 are older), the Classic environment still works on PowerPC Macs. PowerPC Macs that are running 10.5 can't use Classic while booted into 10.5, however can boot into 9 if they were able to before through Apple menu -> System Preferences -> Startup Disk. These Macs are described here:
2. Classic can be restored using the Mac OS 9 disk or restore disks which came with your computer if your computer came with Mac OS X and is able to use Mac OS 9. All PowerPC Macs can use Mac OS 9 in some fashion.
Those released after 2003 for the most part can only use Classic. In order to boot into Mac OS 9 on Macs that can boot Mac OS 9 after an erase and install with Mac OS X, you need to be sure that your erase included the installation of Mac OS 9 drivers:
It is perhaps better if you did this procedure just to run install Mac OS X for the first time after installing the Mac OS 9 drivers, instead of the erase and install function.
3. Before 10.2, retail copies of Mac OS X did include Mac OS 9 retail too. That stopped being the case with 10.2. In addition, with 10.2's release, the Macs no longer included a Mac OS 9 installer disk, and instead had Mac OS 9 put on the restore disks and restorable by this article:
This procedure doesn't work with Intel Macs.
4. Most Mac OS 9 compatible document formats are readable with Mac OS X applications. To find out if yours is, check these search engines for comparable applications, or ask on the board for a comparable application: