/ˈfaɪl ˌsɪstəm/
noun — "organizes storage for data access."
FileSystem is a software and data structure layer that manages how data is stored, retrieved, and organized on storage devices such as hard drives, SSDs, or networked storage. It provides a logical interface for users and applications to interact with files and directories while translating these operations into the physical layout on the storage medium. A file system determines how files are named, how metadata is maintained, how storage space is allocated, and how access permissions are enforced.
Technically, a FileSystem maintains hierarchical structures, commonly directories and subdirectories, with files as leaf nodes. Metadata such as file size, timestamps, permissions, and pointers to physical storage locations are stored in tables, nodes, or inodes depending on the file system design. Common file system types include FAT, FAT32, NTFS, ext4, HFS+, APFS, and XFS, each with optimizations for performance, reliability, concurrency, and scalability. Many file systems implement journaling or transaction logging to protect against corruption from crashes or power failures.
In workflow terms, consider creating a document on a computer. The operating system requests the FileSystem to allocate storage clusters or blocks, update metadata records, and maintain the directory entry. When reading the file, the FileSystem locates the clusters, retrieves the content, and checks permissions. This abstraction ensures that applications do not need to manage the physical layout of bytes on disk, allowing uniform access across different storage devices.
A simplified code example demonstrating file operations through a file system interface:
// Pseudocode for file system usage
fs.createDirectory("/projects")
fileHandle = fs.createFile("/projects/report.txt")
fs.write(fileHandle, "Quarterly project report")
content = fs.read(fileHandle)
print(content) # outputs: Quarterly project report
Advanced file systems support features such as file compression, encryption, snapshots, quotas, and distributed storage across multiple nodes or devices. They often provide caching layers to improve read/write performance and support concurrency control for multi-user access. Distributed and networked file systems like NFS, SMB, or Ceph implement additional protocols to maintain consistency, availability, and fault tolerance across multiple machines.
Conceptually, a FileSystem is like a library with organized shelves, cataloged books, and an indexing system. Patrons and librarians can store, retrieve, and manage materials without needing to know the physical arrangement of every book, while metadata and logs ensure order and integrity are maintained.
See NTFS, Master File Table, Journaling.