From REALbasicWiki

On the Macintosh, each file is composed of a data fork and a resource fork. The latter is a structured piece of data which contains both system-wide and application-specific informations, whose every piece is identified by its type and ID. This particular structure is unique to the Macintosh hard drive format, called HFS+.

The resource fork has been kind of deprecated with Mac OS X, though it still may be helpful in some cases. Before mac OS X (i.e. Mac OS 7 to 9), ResEdit was the software of choice to create or edit resource forks. ResEdit is still usable on PowerPC Macintoshes in the Classic environment. On Intel Macintoshes, however, you will need a software like Rezilla.

[edit] See also

• Resource fork
• ResourceFork class