External Disk Reformatting

TidBITS Talk
17

Yes. Apple has renamed their file systems over the years, but “Mac OS Extended” is what Apple calls HFS+ these days.

The most interesting (at least to me) Apple file systems, supported by various Macs over the years are:

  • Macintosh File System (MFS). The first file system Apple invented for the Mac. Used primarily on 400K floppies although can, in theory, work on hard drives up to 20MB. Key features are that it’s a flat file system - all files reside in the root directory, with folders being an artifact of the GUI, not related to the way the files are stored on the media. This makes performance very bad on large media, making it inappropriate for anything larger than a floppy disk. Apple made MFS support read-only in System 7.6 and dropped it in Mac OS 8.

  • Hierarchical File System (HFS), also known as “Mac OS Standard” or “HFS Standard”, was introduced in System 2.1 as a part of Apple adding hard drive support, HFS has actual subdirectories (hence the “hierarchical” in the name). Apple dropped support in Mac OS X 10.6 (Snow Leopard), but keeping it as read-only until macOS 10.15 (Catalina), 35 years after its introduction.

    Although HFS is not very useful today, Apple dropping read-only support has been problematic, because quite a lot of classic Mac CD-ROMs are formatted with HFS, and are no longer readable without third-party software. Older Mac floppies (especially 1.44M disks, which can be accessed via USB drives) are typically formatted with HFS, because HFS+ has too much overhead to be practical on such small storage devices.

  • HFS+, also known as “Mac OS Extended” or “HFS Extended”, was introduced in Mac OS 8.1 and continues to be supported today.

    Apple designed HFS+ with future expansion in mind, so they did not need to replace it with a new file system in order to support various Mac OS X features, including:

    • Unix file system features (e.g. permissions, hard links and symbolic links)
    • Journaling
    • Case-sensitive filenames
    • Unicode 3.2 decomposition (replacing the 2.1 algorithm previously used)
    • Access control lists (via previously-reserved “inline attribute data records”)
    • Directory hard-linking (to support Time Machine)
    • Compressed files
    • Volume encryption (FileVault 2)

  • Apple File System (APFS) was introduced in macOS 10.12.4 (Sierra) and is Apple’s preferred file system today. It is probably the best to use on SSD media, but has significant performance problems on mechanically-accessed media (e.g. hard drives).

  • ProDOS. This file system was created for the Apple III (and it’s SOS operating system), but was also used for ProDOS on the Apple II series.

    Mac systems 4 though 7.1 included the Apple File Exchange utility, which could copy files to/from ProDOS- and PC DOS/FAT-formatted floppies. Systems 7.1.2 through 9 included PC Exchange (under various names) capable of actually mounting ProDOS and FAT floppies.

    PC Exchange was dropped in Mac OS X, where support for FAT-formatted media became a natively-supported file system, but support for ProDOS media was dropped.

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