- This article is about the concept of a Macintosh resource fork, and the methods of storing it. For the usual file format used by a resource fork, see Macintosh resource file.
Pre-OS X and some OS X Macintosh files have two forks: the data fork, and the resource fork, which is subdivided into resources. Many file formats use the resource fork to store data, stored in Macintosh resource file format.
Resource forks are usually invisible to the end-user on a Mac platform, but when Mac files are placed in a medium where users of other operating systems can see them (e.g., Windows), they are often visible as an additional subdirectory called resource.frk, or else a name with an underscore (_) as its first character (e.g., _MACOSX for OS X files) containing subdirectories and files that parallel the structure of the files they are associated with.
Later (Unix-based) Mac systems used AppleSingle and AppleDouble formats instead of the "classic" resource fork format when using filesystems not supporting direct use of resource forks. This usage continues in some OS X filesystems.
See also Macintosh resource file#References.