Directory (computing)

In computing, a directory, catalog, or folder, is an entity in a file system which can contain a group of files and/or other directories. A typical file system contains thousands of files, and directories help organize them by keeping related files together. A directory contained inside another directory is called a subdirectory of that directory. Together, the directories form a hierarchy, or tree structure.

If you imagine the computer's file system as a file cabinet, high-level directories may be represented by the drawers, while lower-level subdirectories may be represented as file folders within the drawers.

Historically, and even on some modern embedded devices, the filesystems either have no support for directories at all or only have a flat directory structure, meaning subdirectories are not allowed; there is only a group of top-level directories each containing files. The first popular fully general hierarchical filesystem was that of UNIX. This type of filesystem was an early research interest of Dennis Ritchie.

In modern times in Linux and other Unix-like systems, directory structure is defined by the Filesystem Hierarchy Standard.