File Allocation Systems

Interactive visualization of disk space management techniques in modern operating systems

Interactive Simulator

Experiment with different file allocation methods and see how they work in real-time

Configuration

blocks

Manual Block Allocation

Disk Blocks

Click on blocks to mark them as busy before running the simulation

Allocation Details

Select an allocation method and run the simulation to see results

Understanding File Allocation

Learn how operating systems manage files on storage devices

What is File Allocation?

File allocation refers to the methods operating systems use to organize and store files on storage devices. When you save a file, the OS needs to find available space and keep track of where each part of the file is stored.

Why is it important?

Efficient file allocation systems allow for:

  • Optimized storage utilization - maximizing available disk space
  • Fast access times - reducing the time needed to read and write files
  • Minimal fragmentation - preventing performance degradation
  • Reliable storage - ensuring data integrity and recoverability

Allocation Methods Compared

Three primary approaches to organizing files on disk

Sequential (Contiguous)

Files are stored in consecutive blocks on the disk, defined by a starting address and length.

Advantages

  • Simple implementation
  • Excellent read performance
  • Supports both sequential and direct access

Disadvantages

  • External fragmentation
  • Difficult to expand files
  • Requires knowing final file size in advance

Linked List

Each block contains a pointer to the next block in the file chain, forming a linked list structure.

Advantages

  • No external fragmentation
  • Files can grow dynamically
  • No need to declare size at creation

Disadvantages

  • Poor random access performance
  • Storage space wasted for pointers
  • Reliability issues if pointers are damaged
File Allocation Table (FAT)

A variation of linked allocation where all pointers are stored in a separate table at the beginning of the disk.

Indexed

Each file has an index block containing pointers to all blocks belonging to the file.

Advantages

  • Supports direct access without fragmentation
  • Files can grow as needed
  • No block consolidation issues

Disadvantages

  • Index block overhead
  • File size limited by index block size
  • Multiple disk accesses required
Extended Indexing

For larger files, systems may use linked indices, multi-level indexing, or combined schemes (like Unix inodes).