HFS

HFS, short for Hierarchical File System, is a family of file systems developed by Apple for the classic Mac OS. The original HFS was introduced in 1985 as a successor to the Macintosh File System (MFS). It provided a hierarchical directory structure and supported resource forks for storing metadata and additional data separate from the main data stream. The system used a catalog file organized with a B-tree index to improve performance on spinning hard drives of the era.

HFS was later extended as HFS Plus, commonly called HFS+ or Mac OS Extended. Introduced in 1998, HFS+ increased maximum volume and file sizes, added support for Unicode file names, and offered enhancements such as optional journaling and improved reliability. A variant known as HFSX provided case-sensitive semantics, while most consumer deployments used case-insensitive HFS+ by default.

With the shift to newer storage technologies and reliability requirements, Apple introduced Apple File System (APFS) in 2017. APFS became the default filesystem for macOS on new installations and solid-state drives, offering features such as strong encryption, space efficiency through cloning, and snapshots for easier backups. HFS+ remains supported for older volumes and external drives, with read/write access possible, though newer features are not available under APFS.

In modern macOS environments, APFS is recommended for new systems, while HFS/HFS+ persists primarily for compatibility with legacy hardware, time machine backups on older setups, or external drives that were formatted prior to the APFS transition.