MacBinary

MacBinary is a file format that combines the two forks of a traditional Mac OS file into a single file, along with HFS's extended metadata. The resulting file is suitable for transmission over FTP, the World Wide Web, and electronic mail. The documents can also be stored on computers that run operating systems with no HFS support, such as Unix or Windows.

MacBinary was widely supported on the Macintosh and was built into most communications programs on that platform. Similar solutions were built into most data compression applications on the Mac, and although these did not require MacBinary to survive transmission across non-Mac systems, MacBinary was often added in these cases to preserve longer filenames and other features.

The dual-fork nature of the HFS system was not used on Mac OS X, and MacBinary has largely disappeared.

Description

In contrast to other computers of the era, Macintosh applications included both computer code as well as a large number of resources that were used by the operating system (OS) itself. These resources were also widely used in documents to store rich media like sounds and images. However, the resource system had the significant limitation that the maximum size of any single resource was only 32 kB, far too small for storing document data. To address this, Apple introduced the concept of forks, allowing any file in the filesystem to have both a resource fork and a data fork, basically separate files. The OS would ensure the two separate files were always treated as a single object, so dragging it to a floppy disk in the Finder would actually copy both files.