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Definition: HFS


(Hierarchical File System) The previous Mac file system. Although superseded by the Apple File System (see APFS), Macs still format, read and write HFS drives. See APFS.

The first HFS version (Mac OS Standard) was introduced in 1985. HFS+ (Mac OS Extended) came out in 1998 in preparation for Mac OS X, featuring Unicode support and a dramatically increased file size from 2GB to 16TB. In 2003, journaling was added (see journaling file system), and case-sensitive file names were introduced under the HFSX option. Case-sensitive names are a standard feature of Unix, and Mac OS X (later renamed macOS) is based on Unix (see Mac OS X).

Data and Resource Forks
HFS supports two structures: the "data fork" and "resource fork." Just like other file systems, data in the data fork are accessed by an offset into the file; for example: OPEN FILE and READ FROM BYTE 13,904.

The resource fork is unique however. It functions like a mini-database, holding executable code and program elements such as icons, menus and sounds. Having the program's resources in separate structures allows them to be edited independently and more easily localized into different languages. In addition, data files can use the resource fork as a subfolder. For example, a word processor might store text in the data fork while storing images in the resource fork. See APFS, file system and hierarchical file system.




HFS and ExFAT on the Same Drive
This Mac-connected Lacie external hard drive comes with a utility that enables dual formatting. The Mac OS Extended (HFS+) partition is native only to the Mac, whereas exFAT allows the drive to be read and written by Windows PCs.





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