Learn about file systems in one article

The file system plays a key role in the operating system. It is responsible for organizing and managing data on storage media, and at the same time realizing data access and storage functions. Users interact with the system, manage and access data through the file system, which makes data storage and retrieval more efficient and convenient.

Various operating systems are equipped with their own unique file systems, such as NTFS for Windows, ext4 for Linux and APFS for MacOS. In addition, there are also some common file systems, such as FAT32 and exFAT, to facilitate data exchange between different systems. The file system is responsible for dividing and merging physical storage devices to provide a unified logical device for the operating system. It can divide a physical disk into multiple logical partitions, or merge multiple logical partitions into one volume. When volumes are merged across multiple physical disks, the file system implements a logical expansion of the capacity of a single physical device.

Partition and volume diagram

The core function of the file system is to manage and organize files. Each file has a unique path and name, which constitute the file's identity and location in the system. The top level of the file system is a logical partition or logical volume, and files are stored in different directories hierarchically, forming a tree structure.

Tree file structure diagram

In the file system, file access permissions and execution permissions are the main differences between files, and the difference in file content depends on the definition of the file itself. Various file types access their data according to the file protocol, usually declaring the file type in the file header. The format of the file name helps the system and users identify the file type, but it does not change the type and content of the file. In early Windows systems, the 8.3 file name naming standard was adopted, in which the three characters after "." help the system distinguish file types. For example, "exe" represents an executable file.

In addition to the hardware capacity limit in the file system, there is also an upper limit on the number of files. When there are a large number of small files in the system, the number of file indexes in the file system will be exhausted, and new files cannot be created even if there is storage space on the physical disk. When this happens, we need to rely on some application-level file management programs to uniformly manage these small files. In these application-level file management programs, some "large" files of fixed sizes are created, such as 64MB, 128MB, etc. File management programs will store small files in designated locations within these large files. A "large" file in the file system will contain multiple small files. This effectively reduces the number of files in the file system. Although file management programs accessing files may result in reduced access performance and reduced space usage, all files stored in the file system are large. Storing large files can effectively avoid file system fragmentation and performance degradation caused by too many files. It is an effective balancing method.

The file system is the basis of data, including documents, multimedia and database files. Understanding its characteristics is critical to application data storage design and development.

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