View source for Directory (computing)

{{Short description|File system structure for locating files}}
[[File:Dir command in Windows Command Prompt.png|300px|thumb|Screenshot of a [[Microsoft Windows]] [[cmd.exe|command prompt]] window showing a directory listing.|alt=]]

In [[computing]], a '''directory''' is a [[file system]] cataloging structure that contains references to other [[computer file]]s, and possibly other directories. On many computers, directories are known as '''folders''' or '''drawers''',<ref>{{cite book |title=Using The AMIGA Workbench |date=July 1991 |publisher=Commodore-Amiga |chapter=Chapter 1: Tutorial |page=46 |quote=The path specifies the disk name, or location, and all of the drawers that lead to the specified file.}}</ref> [[analogy|analogous]] to a [[workbench]] or the traditional office [[filing cabinet]]. The name derives from books like a [[telephone directory]] that lists the phone numbers of all the people living in a certain area.

Files are organized by storing related files in the same directory. In a [[hierarchical file system]] (that is, one in which files and directories are organized in a manner that resembles a [[tree structure|tree]]), a directory contained inside another directory is called a '''subdirectory'''. The terms '''parent''' and '''child''' are often used to describe the relationship between a subdirectory and the directory in which it is cataloged, the latter being the parent. The top-most directory in such a filesystem, which does not have a parent of its own, is called the '''root''' directory.

The [[freedesktop.org]] media type for directories within many [[Unix-like]] systems&nbsp;– including but not limited to systems using [[GNOME]], [[KDE Plasma 5]], or [[ROX Desktop]] as the desktop environment&nbsp;– is "inode/directory".<ref>{{cite web|url=https://specifications.freedesktop.org/shared-mime-info-spec/shared-mime-info-spec-latest.html#idm45530160423200|title=Shared MIME-info Database|last=Leonard|first=Thomas|at=Non-regular files|date=2018-10-02|publisher=[[X Desktop Group]]|access-date=2023-03-13}}</ref> This is not an [[media type|IANA registered media type]].

==Overview==
[[File:Files11_directory_hierarchy.svg|thumb|Diagram of a hierarchical directory tree. The root directory is here called "MFD", for Master File Directory. Usually a file can only be in one directory at a time, but here File 2 is [[hard link]]ed so it appears in two directories.]] <!-- this Files-11 structure is not a tree, this image has to be replaced, or the problematic link from Dir 3 to File 2 needs to be modified and explained as a symbolic link (Unix parlance) or shortcut (Microsoft Windows parlance). -->
Historically, and even on some modern [[embedded system]]s, the file systems either had no support for directories at all or had only a "flat" [[directory structure]], meaning subdirectories were not supported; there was only a group of top-level directories, each containing files. In modern systems, a directory can contain a mix of files and subdirectories.

A reference to a location in a directory system is called a [[Path (computing)|path]].

In many [[operating system]]s, programs have an associated [[working directory]] in which they execute. Typically, file names accessed by the program are assumed to reside within this directory if the file names are not specified with an explicit directory name.

Some operating systems restrict a [[computer user|user's]] access only to their [[home directory]] or project directory, thus isolating their activities from all other users. In early versions of Unix, the root directory was the home directory of the [[root user]], but modern Unix usually uses another directory such as {{mono|/root}} for this purpose.

In keeping with [[Unix philosophy]], Unix systems treat directories as a type of file.<ref>{{cite web|title=Everything is a File |date=c. 2002 |website=Behavior Genetics Association|url=http://www.bga.org/~lessem/psyc5112/usail/concepts/filesystems/everything-is-a-file.html |url-status=dead |archive-url=https://web.archive.org/web/20120310211947/http://www.bga.org/~lessem/psyc5112/usail/concepts/filesystems/everything-is-a-file.html |archive-date=March 10, 2012 |access-date=April 30, 2021}}</ref> Caveats include not being able to write to a directory file except indirectly by creating, renaming, and removing file system objects in the directory and only being able to read from a directory file using directory-specific library routines and [[system call]]s that return records, not a byte-stream.<ref>{{cite web |url=https://man7.org/linux/man-pages/man3/readdir.3.html |title=readdir(3) — Linux manual page |author=<!--Not stated--> |date=2021-03-22 |publisher=The Linux man-pages project |access-date=November 27, 2022 |quote=}}</ref>

===Folder metaphor===
[[File:Breezeicons-apps-48-system-file-manager.svg|thumb|right|Sample folder icon (from [[KDE]]).]]
The name ''folder'', presenting an analogy to the [[file folder]] used in offices, and used in a hierarchical file system design for the [[Electronic Recording Machine, Accounting]] (ERMA) Mark 1 published in 1958<ref>{{cite journal|last1=Barnard III|first1=G. A.|last2=Fein|first2=L.|title=Organization and Retrieval of Records Generated in a Large-Scale Engineering Project|journal=Proceedings of the Eastern Joint Computer Conference|date=1958|pages=59–63|doi=10.1109/AFIPS.1958.75|url=http://www.computer.org/csdl/proceedings/afips/1958/5053/00/50530059-abs.html}}</ref> as well as by [[Xerox Star]],<ref>{{cite web|url=https://www.youtube.com/watch?v=Cn4vC80Pv6Q/ |archive-url=https://ghostarchive.org/varchive/youtube/20211221/Cn4vC80Pv6Q |archive-date=2021-12-21 |url-status=live|title="Xerox Star User Interface (1982)"|work=YouTube|date=28 August 2009 |access-date=19 November 2014}}{{cbignore}}</ref> is used in almost all modern [[operating system]]s' desktop environments. Folders are often depicted with [[Computer icon|icon]]s that visually resemble physical file folders.

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'').{{OR|date=July 2020}}  For example, [[Microsoft Windows]] uses the concept of [[special folder]]s 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. Many operating systems also have the concept of "smart folders" or [[virtual folder]]s that reflect the results of a file system search or other operation. These folders do not represent a directory in the file hierarchy. Many [[email client]]s allow the creation of folders to organize email. These folders have no corresponding representation in the filesystem structure.

If one is referring to a ''container of documents'', the term ''folder'' is more appropriate. {{cn|date=January 2021}} The term ''directory'' refers to the way a structured list of document files and folders are stored on the computer. The distinction can be due to the way a directory is accessed; on Unix systems, {{mono|/usr/bin/}} is usually referred to as a directory when viewed in a [[command line]] [[Command-line interface|console]], but if accessed through a graphical [[file manager]], users may sometimes call it a folder.

==Lookup cache==
{{expand section|date=December 2013}}
Operating systems that support hierarchical filesystems (practically all modern ones) implement a form of [[Cache (computing)|caching]] to [[Random-access memory|RAM]] of recent [[Path (computing)|path]] lookups. In the [[Unix]] world, this is usually called '''Directory Name Lookup Cache''' (DNLC), although it is called '''dcache''' on [[Linux]].<Ref name="dlnc">{{cite web|url=http://www.citi.umich.edu/projects/nfs-perf/results/cel/dnlc.html|title=Close-To-Open Cache Consistency in the Linux NFS Client|publisher=Citi.umich.edu|access-date=19 November 2014}}</ref>

For local filesystems, cache entries normally expire only under pressure from other more recent entries. For [[distributed file system|network file system]]s a [[Cache coherence|coherence mechanism]] is necessary to ensure that entries have not been invalidated by other clients.<Ref name="dlnc"/>

==See also==
* [[File folder]]
{{col-begin}}
{{col-break|width=33%}}
;Concepts
* [[Directory structure]]
* [[Filename]]
* [[Filesystem Hierarchy Standard]]
* [[Home directory]]
* [[Root directory]]
* [[Virtual folder]]
* [[Working directory]]
{{col-break}}
;Commands
* [[cd (command)]]
* [[chroot]]
* [[dir (command)]]
* [[mkdir]]
* [[pushd and popd]]
* [[pwd]]
* [[tree (command)]]
{{col-end}}

==References==
{{Reflist}}

==External links==
{{Commons category|File system directories}}
* [http://www.linfo.org/directory.html Definition of directory] by The Linux Information Project (LINFO)

{{Computer files}}

{{Authority control}}
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[[Category:Computer file systems]]
[[Category:File system directories| ]]
[[Category:File system management]]