Basic Concepts of Computer File Systems

A computer file system is a method and data structure that an operating system uses to control how data is stored, organized, and retrieved on storage devices. It determines how files are named, structured, and accessed within a storage medium like a hard disk or solid-state drive.

Core Components of a File System

• Files: A named collection of related information recorded on secondary storage.
• Directories: Hierarchical structures containing files and other subdirectories to organize data.
• Metadata: Data about data, including file size, creation date, modification time, owner, and access permissions.

Key Functions of File Systems

• It allocates space on storage media for new files and manages free storage space.
• It enforces security controls and user permissions to restrict unauthorized file access.
• It translates logical file requests from applications into physical disk block addresses.
• It maintains directory structures to allow quick navigation and retrieval of stored data.

Common File System Types

File Allocation Methods

Contiguous Allocation

• Each file occupies a set of contiguous blocks on the storage disk.
• It allows fast sequential and direct access to file data.
• It suffers from external fragmentation and difficulty in expanding file sizes.

Linked Allocation

• Each file is a linked list of disk blocks scattered across the storage medium.
• It eliminates external fragmentation and allows files to grow dynamically.
• It provides slow direct access because pointers must be read sequentially.

Indexed Allocation

• It brings all pointers for a file together into a dedicated index block.
• It supports efficient direct access without external fragmentation.
• It incurs storage overhead for maintaining index blocks.

Important Facts on File Systems

• File Allocation Table was introduced by Microsoft in 1977 for floppy disks.
• New Technology File System was introduced by Microsoft in 1993 with Windows NT 3.1.
• The root directory is the topmost directory in a hierarchical file system structure.
• The Linux ext4 file system supports journaling to prevent data corruption during power failures.
• Journaling file systems maintain a log of changes before writing them to the main storage disk.