You can run the following types of applications under Mac OS X:
Classic applications? Classic applications are those designed to run under previous versions of the Mac OS; however, because of Mac OS X's Classic environment, you can also run these applications under Mac OS X.
Unix applications? Because Mac OS X is based on Unix, you can run many Unix applications on your Mac. Some of these applications have to be recompiled to run on the Mac, but most will work as they are. Of course, you will need to run them from the command line (unless you find and install a graphical user interface for the Unix subsystem). Because Unix is such a prevalent OS, thousands of Unix applications are available for you to use.
Java applications? You can run applications written in the Java and Java 2 programming languages. Because Java is a platform-independent programming language, the same applications work on Windows, Macintosh, and other platforms. You mostly encounter Java applications on the Web, but you will find some standalone Java applications as well.
Carbon applications? These applications are written using the Carbon programming environment, which is designed to take advantage of the Mac OS X architecture. Many are Classic applications that have been ported over to Mac OS X?in Mac OS X-lingo, they have been carbonized. Because carbonizing an application requires considerably fewer resources than does creating a Cocoa application, most Mac OS X applications were carbonized Mac OS 9 applications early in Mac OS X's life. As Mac OS X continues to mature, this will change and the majority of applications will be written specifically for Mac OS X (using Carbon or Cocoa).
Cocoa applications? These applications are written using the Cocoa programming architecture, which means they take full advantage of all the advanced features Mac OS X provides. Cocoa applications have to be written from the ground up in the new environment rather than being ported over as carbonized applications can be. Eventually, most new Mac OS X applications will be based on Cocoa.
To learn about installing and using Classic applications, see Chapter 7, "Working with Mac OS 9, the Classic Environment, and Classic Applications," p. 183.
By the time version 10.3 was released, most major Mac applications were available in Carbon or Cocoa versions. Some are still in the carbonized state.
Because many carbonized applications are applications that were created for earlier versions of the OS and ported over to Mac OS X, some do not meet certain standard Mac OS X interface conventions. For example, some of the Mac OS X standard menus you see in Cocoa applications are not present in carbonized applications.