Macintosh File System

The Macintosh File System (MFS) was the first file system used by Macintosh computers.

Features
MFS was a flat file system where all files were stored by the system on the root level of volumes. However, MFS had a mechanism that allowed users to create the cosmetic appearance of folders in the Finder by renaming the always-present folder "Empty Folder," which would then be re-created.

MFS supported Macintosh files in two parts: a data fork for ordinary file data, and a resource fork for collections of metadata, such as icon bitmaps, user interface elements, program segments, parametric values, and other elements that were stored in attribute/value pairs. Accessing the resource fork from disk instead of keeping the contents in RAM helped reduce memory requirements for the original Macintosh 128K. Additional metadata was stored in a hidden resource database file called Desktop.

Shortcomings
Folders within folders were not supported. Since the directory of files was still stored in RAM, the Macintosh 128K was known to slow down and run out of memory if too many files were on a drive, such as the Macintosh Hard Disk 20. One workaround was to partition hard disks.

Support
MFS was the native file system for early compact Macs running System 1 and 2 from 400 KB floppy disks. It internally supported filenames up to 255 characters, but the Finder only supported 63 characters. On September 17, 1985, it was superseded by the Hierarchical File System (HFS) in System 2.1, which reduced the file name limit to 31 characters. Support for 255 character file names returned in HFS Plus, which was introduced with Mac OS 8.1 on January 19, 1998. However, the Finder's 31-character limit was not revised until Mac OS X.

Deprecation
System 7 began to phase out support for MFS by first eliminating cosmetic folders and removing the ability to rename MFS volumes. System 7.5 removed the ability to format new volumes with MFS. However, due to problems with maintaining backwards compatibility with MFS volumes, they became read-only in Mac OS 7.6.1 and support was dropped in Mac OS 8. However, the ability to format and copy MFS floppies was retained by Disk Copy, even up to a "Beige" Power Macintosh G3 running Mac OS 8 or 9; MFS volumes are stored as   image files.

Apple provided sample code of a VFS plug-in called MFSLives to provide read-only access of MFS volumes by Mac OS X 10.4 or later. Apple does not provide the compiled binary itself, but archival websites provide the   file, which can be placed into   (no rebooting is required, but permissions will need to be repaired). Vintage   images can be renamed to   and opened directly as read-only volumes in the Finder.