With Mac OS X, you may hear programmers refer to Cocoa, Carbon, and Classic applications. But what exactly do those terms mean, and why are they important to the average user? Here's a brief rundown of each type of application.

• Cocoa applications: Cocoa is the Mac OS X application development environment — in other words, programmers use Cocoa to create Mac OS X applications. These apps are built from the ground up in Mac OS X and require Mac OS X to work. They do not work in Mac OS 9.x or earlier versions.
• Carbon applications: Programmers often say that their applications have been "Carbonized." Carbon applications used to run only in Mac OS 9.x and earlier, and have since been updated to run natively in Mac OS X, as well, without having to use Mac OS X's Classic environment.
• Classic applications: These programs have not been converted over to Mac OS X as yet; you have to either reboot into Mac OS 9 to run them or launch them in Mac OS X's Classic environment. They do not run natively in Mac OS X.

Cocoa and Carbon applications gain the benefits of Mac OS X's protected memory, preemptive multitasking, multithreading, and built-in multiprocessor support. Classic applications cannot benefit from these Mac OS X features, although the Classic environment (as a Mac OS X application) does. Thus, if something crashes inside the Classic environment and results in the crash of Classic, your other Mac OS X apps continue to run.