On the Macintosh, all files have two parts: a resource fork and a data fork. The data fork usually contains information (that is, the actual data) that the program needs to run. The resource fork usually contains the instructions for running a program or other necessary resource information, such as fonts, icons, menus, and so on.
Some files on the Macintosh store their information in two different "forks," a data fork and a resource fork. The data fork usually contains the main body of the file's information, such as the text or graphic data that make up the file. The resource fork contains special Macintosh information. Most cross-platform files, such as HTML files, JPEG files, and Microsoft Word files, have just a data fork. See the upload formats help topic for a discussion of forks and how they relate to transferring files.
system software: The part of a document where user-generated data is stored (as opposed to the resource fork, where the application's own information is stored).