Linked vs. Multilevel Indexed File Allocation: A Comparison

Understand the differences between linked and multilevel indexed file allocation methods. This guide compares their performance characteristics, including storage efficiency, random access speed, and implementation complexity. Learn how these techniques manage files larger than a single disk block in file systems.

Linked and Multilevel Indexed File Allocation

Introduction to Linked and Multilevel Indexed Allocation

In file systems, allocation methods determine how a file's data is stored on a disk. Both linked and multilevel indexed allocations are techniques designed to handle files larger than a single disk block (a fixed-size unit of storage). These methods use pointers or indices to chain together multiple blocks, allowing for files of virtually any size. The choice between them involves a trade-off between storage efficiency, speed of random access, and complexity of implementation.

Single-Level Linked Indexed Allocation

In single-level linked indexed allocation, a file's data is spread across multiple disk blocks. The file's index block contains pointers to these data blocks. For larger files than what fits into a single index block, the last entry in the index block contains a pointer to another index block, effectively creating a linked list of index blocks. This approach allows for files that exceed the size capacity of a single index block.

Diagram of Single-Level Linked Indexed Allocation

Advantages

  • Overcomes file size limitations of single-level indexed allocation.

Disadvantages

  • Random access to data blocks is slower (requires traversing the linked list of index blocks).

Multilevel Indexed Allocation

Multilevel indexed allocation uses multiple levels of index blocks to point to data blocks. The first-level index block points to second-level index blocks, which in turn point to data blocks. This hierarchical approach provides efficient random access to data for very large files while minimizing the number of disk accesses required.

Diagram of Multilevel Indexed Allocation

Advantages

  • Improved random access compared to single-level linked indexed allocation.

Disadvantages

  • Higher access time compared to single-level indexed allocation due to multiple levels of indirection.