How is a fat like linked allocation?

The MS-DOS File Allocation Table (FAT) is a collection of linked lists maintained separately from the files. One entry for each block on the disk. Each directory entry holds the block number of the file’s first block. This number is also an index into the FAT.

How does indexed allocation work?

Instead of maintaining a file allocation table of all the disk pointers, Indexed allocation scheme stores all the disk pointers in one of the blocks called as indexed block. Indexed block doesn’t hold the file data, but it holds the pointers to all the disk blocks allocated to that particular file.

What are the advantages of contiguous allocation?

The advantages of contiguous allocation are:

• The contiguous allocation method gives excellent read performance.
• Contiguous allocation is easy to implement.
• The contiguous allocation method supports both types of file access methods that are sequential access and direct access.

What is contiguous allocation in operating system?

In the Contiguous Memory Allocation, each process is contained in a single contiguous section of memory. In this memory allocation, all the available memory space remains together in one place which implies that the freely available memory partitions are not spread over here and there across the whole memory space.

How does linked allocation work in a file?

With linked allocation, each file is a linked list of disk blocks; The disk blocks may be scattered anywhere on the disk. The directory contains a pointer to the first and last blocks of the file. For example, a file of five blocks might start at block 9 and continue at block 16, then block 1, then block 10, and finally block 25 (see Fig. 9 ).

Is there external fragmentation in linked list allocation?

There is no external fragmentation with linked allocation. Any free block can be utilized in order to satisfy the file block requests. File can continue to grow as long as the free blocks are available. Directory entry will only contain the starting block address. Random Access is not provided. Pointers require some space in the disk blocks.

How are pointers allocated in a linked scheme?

However, in linked allocation we lose the space of only 1 pointer per block. For files that are very large, single index block may not be able to hold all the pointers. Linked scheme: This scheme links two or more index blocks together for holding the pointers. Every index block would then contain a pointer or the address to the next index block.

What are the disadvantages of indexed allocation?

Disadvantages: For very small files, say files that expand only 2-3 blocks, the indexed allocation would keep one entire block (index block) for the pointers which is inefficient in terms of memory utilization. However, in linked allocation we lose the space of only 1 pointer per block.