Mac OS X is inherently more stable than what most Mac users are used to, but those of us who rely on Classic apps have experienced crashes with those apps. When that happens, Classic becomes unusable until you force the recalcitrant app to quit. Until now however, if you needed to force quit a Classic app, any attempt to do so basically shut down the entire Classic environment. We discovered that one of the undocumented features in Mac OS X 10.0.4 is the ability to force quit individual Classic apps without bringing down the entire environment.
If you are having a problem with Classic apps crashing, do the following. If you can kill the app, Classic is fine. The usual way to do this has been a Option-Command Escape, which killed the active app in Classic. In Mac OS X, it actually brings up a process listing (process = running application).
The Process List you get when you hit Option-Command-Escape.
Double click on an app in this list, and Mac OS X will ask you if you want to Quit or Force Quit it. If Classic has crashed, then all of your Classic apps will come down too. If it is just the one app within Classic that has crashed, it will quit nicely and you can go on about your business.
Earlier this month, we mentioned another nifty feature of OS X, the ability to force quit an app from the Dock. If you Control-Option-Click on a running app in the Dock, you get the option of Force Quitting instead of just Quitting. This also works for individual Classic apps in 10.0.4 as described above. (Thanks to the Observers who helped with this item!)
Kudos to Apple for furthering their efforts to make working with Classic as seamless as possible. This is a good feature for them to have added. Being able to Force Quit individual Classic apps is vital to those of us who still need to run Classic apps to get our jobs done.
Bonus Tip: I recommend that you keep CPU Monitor open, especially if you run Classic apps. CPU Monitor is a nifty app included with Mac OS X that monitors your CPU usage (hence the name). Whether running in "expanded" mode or in the default mode, the graph in CPU Monitor can show you when you have a run away program or a Classic app that has crashed. This is because Classic apps that crash tend to send Classic into a death spiral that hogs all of the CPU power they can get, and the graph becomes maxed out. This can also happen with your Mac is working on something legitimate that is processor intensive, but the maxed graph will subside as soon as that task is done. If it never subsides, and you canit use Classic, you probably have a run away process. See the below image for an example. The red lines are "root" processes, or tasks that belong to the operating system. The yellow lines are user processes, or tasks that belong the apps that I am running. The gray area is unused processor time. Note that I changed the colors in the CPU Monitor Prefs to make them look this way. The default colors are more "puke" oriented. :-)
CPU Monitor in "expanded" mode.