5.1.2 Describe The Various Methods of Storing Files

5.1.2 Describe the various methods of storing files

Contiguous allocation

Each file occupies a set of contiguous blocks on the disk.
Simple only starting location (block #) and length (number of blocks) are required.
Random access.
Wasteful of space (dynamic storage allocation problem).
Files cannot grow.

Linked List Allocation (disc block)

Each file is a linked list of disk blocks: blocks may be scattered
anywhere on the disk.
Simple – need only starting address.
Free-space management system – no waste of space.
No random access.
Mapping.

Linked list allocation using index (table in main memory)

Allow direct record acess.

Every file has own index block.

Support sequential and direct access.

Does not necessarily improve storage space use.

Larger file experience several index levels.

Indexed Allocation

Brings all pointers together into the index block.
Logical view.
Need index table
Random access
Dynamic access without external fragmentation, but have overhead of index block.
Mapping from logical to physical in a file of maximum size of 256K words and block size of 512 words. We need only 1 block for index table.

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