Chapter 14: File-System Implementation: Allocation Methods and Free-Space Management

File-System Implementation: Allocation Methods and Free-Space Management begins by discussing file-system structure, including the boot control block, volume control block, and per-file file control blocks (FCBs), along with in-memory data structures for caching metadata. The chapter explains allocation methods—contiguous, linked, and indexed—highlighting their trade-offs in performance, fragmentation, and access speed. It examines free-space management techniques such as bitmaps, linked lists, and grouping, and shows how these methods affect allocation efficiency. Directory implementation strategies are discussed, including linear lists and hash tables for faster lookups. File-system mounting and the role of virtual file systems (VFS) are introduced as abstractions that allow multiple file-system types to coexist within a single OS. The chapter also covers recovery techniques, including consistency checking, journaling, and log-structured file systems, which help maintain reliability after crashes. Examples from UNIX (with inodes) and Windows NTFS illustrate how different systems implement core file-system operations. By the end, readers understand the detailed data structures, algorithms, and management strategies that make file-system operations fast, reliable, and scalable.