MFS

Macintosh File System (MFS) is a volume format (or disk file system) created by Apple Computer for storing files on 400KB floppy disks. MFS was introduced with the Macintosh 128KB in January 1984.
MFS was notable both for introducing resource forks to allow storage of structured data as well as for storing metadata needed to support the graphical user interface of MacOS. MFS allows file names to be up to 255 characters in length, although Finder does not allow users to create names longer than 63 characters. MFS is called a flat file system because it does not support folders.
Apple introduced Hierarchical File System, or HFS as a replacement for MFS in September 1985. In MacOS 7.6.1, Apple removed support for writing to MFS volumes, and in MacOS 8, support for MFS volumes was removed altogether.