HFS (Hierarchical File System) is a file system developed by Apple Inc. for early Macintosh computers, introduced in 1985 to replace the Macintosh File System (MFS). Its key innovation was the introduction of a hierarchical directory structure, allowing files to be organized into folders and subfolders. HFS uses a B-tree–based catalogue to manage file and directory metadata and supports Macintosh-specific features such as data forks and resource forks. However, HFS was designed for the relatively small storage capacities of the 1980s and did not scale efficiently as disk sizes increased.
To address these limitations, Apple introduced HFS+ (Hierarchical File System Plus) in 1998. HFS+ improved space efficiency by reducing allocation block sizes, supported Unicode file names, and allowed much larger volumes and files than HFS. It retained compatibility with core Macintosh file concepts while significantly improving performance and scalability. HFS+ became the default file system for Mac computers for many years, until it was ultimately replaced by APFS (Apple File System) beginning in 2017.