(1) The method for storing and retrieving files on a disk. It is system software that takes commands from the operating system to read and write the disk clusters (groups of sectors). The file system manages a folder/directory structure, which provides an index to the files, and it defines the syntax used to access them (how the "path" to the file is coded). File systems dictate how files are named as well as the maximum size of a file or volume.

There are numerous file systems in use; for example, FAT32 and NTFS are Windows file systems, and HFS is used on Macs. Linux uses ext2, ext3 and FAT32. Unix systems use UFS, ext2, ext3 and ZFS. See cluster, path, FAT32, NTFS, HFS, NFS, UFS, ext, ZFS and hierarchical file system.

(2) A data processing application that manages individual files. It opens, closes, reads and writes the file as a single entity. In a file system, files are related to each other by customized programming (customers to orders, vendors to purchases, etc.). Contrast with a "relational database," which has built-in constructs that can more easily form these relationships. For example, they can be used to join files together and split them apart, all without tedious programming. See relational database and DBMS.