Indexed file allocation

Indexed Allocation:
 In Linked Allocation the pointers along with the blocks were scattered across the disk and needed to be retrieved in order by visiting each block for accessing the file.
 To solve this problem Indexed Allocation is used.
 In indexed allocation method, all the pointers are gathered together into one location known as Index Block.
 Each file has its own index block which stores the addresses of disk space occupied by the file.

 Directory contains the addresses of index blocks of files.
 When a file is created initially, all pointers in the index block are set to null value.
 As new blocks are written, the pointers are modified accordingly.

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Advantage:  Indexed allocation supports direct access and does not suffer from any external fragmentation.
Disadvantage:  Indexed allocation suffers from the problem of wasted space.

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