File System In Operating Systems

File System In Operating System

File system manages how data is to be stored or fetched. Files are logically divided into blocks and these blocks are then mapped onto the sectors in a hard disk. This mapping may or may not be contiguous.

File Attributes & Operations

File Operations	File Attributes
1. Creation	1. Name
2. Reading	2. Extension(type)
3. Writing	3. Identifier
4. Deletion	4. Location
5. Truncating	5. Size
6. Repositioning	6. Modified Date, Created Date
	7. Protection/Permission
	8. Encryption, Compression

File Allocation Methods

Contiguous Allocation
Non-Contiguous Allocation - Linked List Allocation, Indexed Allocation These methods aim for efficient disk utilization and faster access times.

Contiguous File Allocation

Advantages

Easy to implement.
Excellent read performance.

Disadvantages

Disk will become fragmented.
Difficult to grow file.

Linked List File Allocation

Advantages

No external fragmentation.
File size can increase.

Disadvantages

Large seek time.
Random acess/Direct acess difficult.
Overhead of Pointers.

Indexed File Allocation

Advantages

Supports direct access.
No external fragmentation.

Disadvantages

Pointer overhead(high number of pointers used).
Multilevel Index(for very large files).

Unix Inode Structure

Unix Inode is a data structure that contains File attributes, direct blocks, single indirect blocks, double indirect blocks and triple indirect blocks. It is a hybrid approach that overcomes the shortcomings of the previous file allocation methods. 'I' is Index, 'Node' is the block in Inode.