Indexed allocation is a modification of linked allocation where the disk block pointers for a file are placed in an index block. The index block has one entry for each portion allocated to the file, and the file allocation table entry for a file points to its index block, allowing for no external fragmentation, efficient random access, and easy mapping of bad disk blocks.

1. Indexed Allocation
A modification of linked allocation where
the disk block pointers for a file are all
placed in an index block.
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2. Example of Indexed Allocation
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3. Indexed Allocation
• File allocation table contains a separate one
level index for each file
• The index has one entry for each portion
allocated to the file
• File indexes are not stored as part of file
allocation table
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4. Indexed Allocation
• File indexes are stored in separate block and the
entry for the file in the file allocation table points to
that block
• Allocation may be on basis of either fixed size block
or variable size blocks
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5. Indexed Allocation Advantages
• No external fragmentation
• provides efficient random access
• Easily map bad disk blocks
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6. Indexed Allocation Advantages
• No external fragmentation
• provides efficient random access
• Easily map bad disk blocks
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