Directory structure

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Directory structure of various operating systems

A directory structure (also called directory tree or folder structure ) is the hierarchical structure of the entire file system of a single computer in the narrower sense and a directory service for any objects (such as users, devices, services, file shares and packages ) in a company network. A tree structure that starts at a root and then branches out at will is common. The directory structure of a file system is described below; for the directory service of a company network, see there.


Both files and directories can be located in each level of the tree ; the latter form the next level of the tree. The directory structure results from the fact that directories can in turn contain (sub) directories, starting from a root directory . The name and position of each entry (file or (sub-) directory) can be specified by specifying a corresponding path that starts at the root and lists all the directories to be run through.

Example: In the figure opposite there is the file in the Unix tree /home/anwendername/Foto.png, i.e. starting from the root directory /in its subdirectory home, anwendernamethe file is located below it in the subdirectory Foto.png.

The possibility of creating cross-connections - i.e. folder or file links , even across levels - turns the tree shape of the directory structure into a network , because the strict hierarchy is lost. Correspondingly, the same file can under certain circumstances be specified using different paths.

Restrictions on a single level (trivial tree) are known from embedded systems . Older file systems, some of which are still used on mainframes , have a relatively rigid directory structure, with some precisely defined number of levels, without the possibility of quickly creating subdirectories.


The first authorization concepts simply gave each user their own directory above the root level. You can still find echoes from this time in the special root user account under Unix, which initially has all system permissions. Although the Unix authorization concept, which is still in common use today, still maintains a close connection to the directory structure, per directory (and per file) for a user (the owner), for a defined group of users, and for all the rest of them an authorization is assigned. A real n: m assignment (i.e. the assignment of rights / prohibitions for each user separately) between directories or files and authorized user accounts is not yet possible if you don't want to create a separate group for each directory. Newer solutions such as ACLs offer more convenient options.


Many operating systems offer the possibility of disks and disk systems to partition . Such partitions, as well as entire disks, can be formatted with a file system, that is, an empty directory structure is created and the allocated disk space is placed under the management of the file system.

Individual file systems can be mounted ("mounted") under Unixoid systems (e.g. BSD , System V , Linux , OS X ) at any point within the directory structure of the computer and then supplement the tree with another branch that may branch in itself. Its origin is also known as the mount point . Other operating systems, such as DOS , Microsoft Windows or OpenVMS , give each file system its own name, so that several trees exist side by side. Since Windows 2000, NTFS mount points can also be used in its file system .

Recent developments in file systems may expose some relational database or object-oriented structuring techniques . Conventional directory structures with a hierarchical system are then one of several options for creating, changing, retrieving and reading data.


Mainly in the area of ​​the Unixoid systems there are efforts to standardize the directory structure independently of the used operating system. A uniform directory structure means that, for example, certain executable files or configuration files can always be found in the same location, which greatly simplifies software development, migration from one operating system to another and the familiarization of users. In addition to the POSIX , SUS and LSB standards, which all also describe the directory structure, the Filesystem Hierarchy Standard (FHS) is an important standardization of a directory structure.

Individual evidence

  1. Aeleen fresh: Unix system administration . O'Reilly Germany, 2003, 2: The Unix Philosophy, p. 66, footnote 13 ( full text in Google Book Search - here the term "file system" refers to the higher-level directory tree.): "The term file system thus relates on the one hand to the higher-level directory tree of the system, which includes all hard drive partitions of the system, which the users can access (as in "the Unix file system"), and on the other hand to the files and directories on the individual hard disk partitions (as in "setting up a file system on a hard disk partition" or "mounting the user file system"). Only from the context does it become clear which of the two meanings of the term is meant. "
  2. Inside Win2K NTFS, Part 1 . MSDN (English)