FFS (Fast File System) is an advanced file system introduced in AmigaOS to replace the OFS (Old File System), specifically optimized for hard drive storage. It dramatically improves performance by using bitmap allocation blocks to track free space rather than scanning the entire disk structure, and stores file metadata in dedicated header blocks rather than with each data block. Introduced as an optional component in AmigaOS 1.3 and becoming the default in AmigaOS 2.0, FFS supports larger partitions, hard and soft links, and became the foundation for later extensions like directory caching and long filenames in AmigaOS 3.0+.