File system
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File system
A file system is the method an operating system uses to control how data is stored and retrieved on a storage device, like a hard drive or SSD. It acts as a crucial layer between the raw storage hardware and the user or applications trying to access files. Essentially, it organizes digital information into a logical structure, making the contents of a storage device usable and understandable.
Without a file system, a storage device is just a collection of data blocks with no way to identify individual files. The file system provides the rules, structure, and tools to manage files and folders, track their locations, record their sizes and other details, and handle access permissions. It translates the folders and files you see into the actual physical addresses where the data sits on the storage media.
Purpose and Role
The main purpose of a file system is to make storage devices usable by systematically managing data. Its key roles include:
Organizing Data: Structuring the storage into directories (folders) and files, usually in a hierarchical (tree-like) structure, to logically group information. Tracking File Locations: Keeping a record of where each part of a file is physically stored on the device. Files are often broken into smaller blocks, and the file system tracks all blocks belonging to a specific file. Managing Metadata: Storing essential information about each file and directory, such as its name, size, creation date, modification date, owner, and access permissions. This is separate from the file's content. Providing an Interface: Offering operations for the operating system to interact with storage, like creating, reading, writing, deleting, moving, or renaming files and directories. Managing Free Space: Keeping track of which areas on the storage device are used and which are available, preventing new data from overwriting existing files. When your operating system wants to open a file, it asks the file system by its path and name, rather than knowing the exact physical location. The file system then finds the file's metadata, determines which physical blocks hold the data, and tells the device to retrieve them.
Key Concepts
File: The basic unit managed by the file system; a named collection of related data treated as one item by users and applications. Directory (Folder): A special container used to group other files and sub-directories, creating a logical structure for data. Path: A text string that shows the location of a file or directory within the file system's hierarchy, like a map from the root to the item. Metadata: Information that describes a file or directory, such as its name, size, type, timestamps, ownership, and permissions. This is managed by the file system and is separate from the file's actual content. Mounting: The process where an operating system makes a file system on a storage device accessible within the OS's directory tree. Block / Sector: The fundamental units of physical storage on the device. The file system manages and allocates these to files and metadata.
Data Integrity and Reliability
Different file systems have features to improve data integrity and reliability. Some modern file systems use journaling, where changes are logged before being applied to the main file system structure. This helps the file system recover more quickly and consistently after power loss, reducing data corruption. Features like checksums can also help detect errors in data blocks.
A robust file system is critical because if its own structures become corrupted, the data on the device might become inaccessible or lost, even if the physical storage media is undamaged. Properly "unmounting" or "ejecting" storage devices ensures the file system finishes all pending write operations before the device is disconnected.
Types of File Systems
Many file systems have been developed, each with different design goals and optimizations. They vary in structure, features, performance, and compatibility with operating systems. Some are designed for specific media (like optical discs or flash drives), while others are general-purpose for hard drives and SSDs. Their design impacts factors like maximum file size, storage volume size, performance for different data access patterns (e.g., many small files vs. few large files), and support for features like permissions, journaling, or encryption.
