Final answer:
The three methods of file allocation are chained, indexed, and contiguous allocation. Contiguous allocation stores files in a contiguous block, offering quick access but potential fragmentation issues.
Step-by-step explanation:
The three methods of file allocation commonly used in file systems are: chained (also known as linked or contiguous allocation), indexed, and contiguous allocation. Chained allocation links the blocks of a file like a chain, with each block pointing to the next block. Indexed allocation uses an index block that contains pointers to all the blocks of a file, allowing for non-sequential blocks to be used efficiently. Contiguous allocation, on the other hand, stores each file as a contiguous block of data on the storage medium, reducing access time but creating issues with fragmentation over time.
The three methods of file allocation commonly used are chained, indexed, and extbf{contiguous allocation}. Contiguous allocation assigns continuous blocks of space to a file. This means that the file is stored in a single, unbroken block of memory. An example of contiguous allocation is the Allocation Table (FAT) used in the FAT file system.