Linked List Allocation in File Systems: Overcoming Contiguous Allocation Limitations
Learn about linked list allocation, a file storage method that addresses the limitations of contiguous allocation. This tutorial explains how linked lists use pointers to chain together file blocks, improving disk space utilization and flexibility in storing files on a disk.
Linked List Allocation in File Systems
Understanding Linked List Allocation
Linked list allocation is a method for storing files on a disk that addresses some of the limitations of contiguous allocation. In contiguous allocation, all blocks of a file must be stored in adjacent locations on the disk. Linked list allocation eliminates this restriction by using pointers to chain together the blocks of a file. The blocks do not need to be physically next to each other on the disk.
How Linked List Allocation Works
In this scheme, each block of a file contains a pointer to the next block in the file. The first block's address is stored in the directory entry. To access the file, you follow the chain of pointers from one block to the next. This approach overcomes the need for contiguous disk space, making it more flexible and potentially more efficient in terms of disk space utilization.
Advantages of Linked List Allocation
- No External Fragmentation: Free blocks can be used efficiently; there's no wasted space between files.
- File Growth: Files can grow easily as long as free blocks are available.
- Simple Directory Entries: Only the starting block address needs to be stored in the directory.
Disadvantages of Linked List Allocation
- No Random Access: Accessing a specific part of the file requires traversing the linked list from the beginning, resulting in slow access times.
- Pointer Overhead: Space is needed to store pointers in each block.
- Susceptibility to Corruption: If a pointer is corrupted or lost, it can make the rest of the file inaccessible.
- Sequential Access Only: Data blocks must be accessed sequentially by following the chain of pointers.