File Allocation Methods

File allocation methods determine how operating systems assign disk space to files. The main allocation techniques include contiguous allocation (each file occupies a contiguous set of blocks), linked allocation (each file is a linked list of blocks), indexed allocation (a separate index block contains pointers to all file blocks), and combined approaches used in modern file systems. Contiguous allocation offers excellent read performance but suffers from external fragmentation and file growth challenges. Linked allocation eliminates external fragmentation but has poor random access performance and reliability issues. Indexed allocation provides efficient random access but requires overhead for storing index blocks. Modern file systems often use variations like linked indexed allocation (multi-level indexes) or extent-based allocation (storing ranges of contiguous blocks). The choice of allocation method affects disk utilization, access performance, reliability, and support for file operations like appending and truncating. File systems also need efficient methods for managing free space, typically using bitmaps (each bit represents a block's allocation status) or linked lists of free blocks. Understanding allocation methods is crucial for file system designers and storage engineers to optimize performance and reliability for specific workloads.