In computing, a directory, catalog, or folder^[1] is an entity in a file system which contains a group of files and/or other directories. A typical file system may contain thousands (or even hundreds of thousands) of directories. Files are kept organized by storing related files in the same directory. A directory contained inside another directory is called a subdirectory of that directory. Together, the directories form a hierarchy, or tree structure.

Overview

A computer's file system can be visualized as a file cabinet, where high-level directories are represented by the drawers and 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 Unix-like systems, especially Linux, directory structure is defined by the Filesystem Hierarchy Standard.

In many operating systems, programs have an associated current working directory in which they execute. Typically filenames accessed by the program are assumed to reside within this directory if the filenames are not specified with an explicit directory name.

Some operating systems restrict a user's access to only their home directory or project directory, thus isolating their activities from all other users.

On Unix, directories are regarded as a type of file.^[2]

The folder metaphor

The name folder, presenting an analogy to the file folder used in offices, is common on most modern operating systems' desktop environments including Mac OS, Mac OS X, Microsoft Windows, and many environments for BSD and Linux. Folders are often depicted with icons which visually resemble physical file folders.

Strictly speaking, there is a difference between a directory which is a file system concept, and the graphical user interface metaphor that is used to represent it (a folder). For example, Microsoft Windows uses the concept of special folders to help present the contents of the computer to the user in a fairly consistent way that frees the user from having to deal with absolute directory paths, which can vary between versions of Windows, and between individual installations.

References

See also

• chdir command
• Filename
• mkdir command
• Working directory
• Web directory

External links

• Definition of directory by The Linux Information Project (LINFO)