indexed allocation - TarisMajor/5143-OpSystems GitHub Wiki

Indexed allocation is a file storage method that uses an index block to keep track of the locations of all the blocks that a file occupies. Unlike contiguous and linked allocation, indexed allocation provides a more efficient and flexible way to manage files, especially when files are not stored in contiguous blocks.

1. Index Block: Each file has an associated index block that contains pointers to all the data blocks of the file. The index block itself is stored on the disk.
2. Non-contiguous Storage: Data blocks of a file can be stored anywhere on the disk. The index block maintains the order and locations of these blocks.
3. Direct Access: With indexed allocation, direct access to any block of a file is possible by using the index block.

1. No External Fragmentation: Since data blocks do not need to be contiguous, there is no external fragmentation. Files can grow dynamically by adding new blocks anywhere on the disk.
2. Random Access: Indexed allocation allows random access to any block of a file. By reading the index block, the system can directly access any data block, making it efficient for various access patterns.
3. Flexible File Management: The use of index blocks makes it easy to manage files of varying sizes. Large files can be accommodated by adding more pointers in the index block or using multiple index blocks if needed.

1. Index Block Overhead: The index block introduces additional overhead as it requires extra disk space to store the pointers. For large files, the index block itself can become large.
2. Pointer Indirection: Every data access requires reading the index block first, which adds an extra level of indirection and can slightly affect performance.
3. Complexity: Managing index blocks and ensuring their integrity adds complexity to the file system implementation.

1. General-Purpose File Systems: Suitable for general-purpose file systems where files vary widely in size and access patterns. Examples include operating system file systems like ext4, NTFS, and others.
2. Database Systems: Ideal for database systems that require efficient random access to records, which may not be stored contiguously.
3. Large Files: Useful for applications that deal with large files, such as media files or scientific data sets, where flexibility in file growth and efficient access are important.

• Operating System Concepts by Abraham Silberschatz, Peter B. Galvin, and Greg Gagne
• File System Interface - GeeksforGeeks
• Modern Operating Systems by Andrew S. Tanenbaum
• Wikipedia - File System
• ChatGPT