If, like me, you came to the Mac in the past five years or so, you may not be aware of the fact that “Mac OS” wasn’t always followed by the letter “X”—sorry, the number ten. But the Mac did have a long and illustrious life before it gained its current UNIX underpinnings. Part of this legacy has lived on—on PowerPC Macs, at least—in the Classic environment.
Classic has never been available on Intel Macs, but as of Leopard, PowerPC Macs will also have to do without Classic, according to this Apple support page, which I’ll quote for you in its entirety:
Classic applications do not work on Intel processor-based Macs or with Mac OS X 10.5.
Upgrade your Mac OS 9 applications to Mac OS X versions. Check with an application’s manufacturer for more information.
So, if you have a PowerPC Mac that still has some Classic applications on it and you intend to go out and get the new cat tomorrow, I suggest that tonight, you pour a tall glass of your beverage of choice. Then, sit down in front of your Mac, and start those trusty Mac OS 9 applications up one more time, and remember the good times. After that, start your overnight full backup and turn in early, because Leopard will be your middle-aged PowerPC Mac’s last chance to be a youthful kitten again: few people expect the next Mac OS X after 10.5 to run on the PowerPC.