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Comparison of docks in Avant Window Navigator on Linux, Mac OS X Leopard, and Sun Microsystems's Project Looking Glass

The Dock in Mac OS X is an application; this is its icon.

The Dock is a graphical user interface feature used to launch applications and switch between running applications. The first appearance of the dock concept was the Iconbar in Arthur.[1] Another early appearance was in the NeXTSTEP and OPENSTEP operating systems and modified for Mac OS X where it behaves more like Apple's Newton OS Dock. There are now many dock applications for many different operating systems.

OPENSTEP Dock

In NeXTSTEP and OPENSTEP, the Dock is an application launcher that holds icons for frequently used programs. The icon for the Workspace Manager and the Recycler are always visible. The Dock indicates the program's current state (running or not running) by showing an ellipsis below its icon if the program is not running and nothing if it is currently running. (Contrast this behavior with the Dock in OS X which uses a triangle or dot to indicate that the program is running and nothing if it has not yet been launched.)

It has been suggested that Mac_OS_X#Criticism be merged into this article or section. (Discuss)

In OS X, however, the Dock is used as a repository for any program or file in the operating system. It can hold any number of items and resizes them dynamically to fit while using magnification to clarify smaller resized items. It can be placed (as in the picture to the left) on the left, on the right, or default on the bottom edge of the screen. Applications that do not normally keep icons in the Dock will still appear there when running and remain until they are exited. These features are unlike those of the dock in the NeXT operating systems where the capacity of the Dock is dependent on display resolution. This may be an attempt to recover some Shelf functionality since OS X inherits no other such technology from NeXTSTEP. (Some Shelf functionality was previously implemented in finder.)

The changes to the Dock bring its functionality also close to that of Apple's Newton OS Button Bar, as found in the MessagePad 2x00 series and the likes. Applications could be dragged in and out of the Extras Drawer, a Finder-like app, onto the bar. Also, when the screen was put into landscape mode, the user could choose to position the Button Bar at the right or left side of the screen, just like the Dock in Mac OS X.

The OS X Dock also has extended menus that control applications without making them visible on screen. On most applications it has simple options such as Quit, Keep In Dock, Remove From Dock, and other options, though some applications use these menus for other purposes, such as iTunes, which uses this menu as a way for a user to control certain playback options. Other Applications include changing the status of an online alias (MSN, AIM/iChat etc.) or automatically saving the changes that have been made in a document (There is no current application with this feature made available for Mac OS X). Docklings can also be opened by using the right-mouse button, if the mouse has one, but most of the time either clicking and holding or control-click will bring the menu up.

The earliest known implementation, called the Iconbar, has been a fundamental part of the RISC OS operating system and its predecessor Arthur since its inception in 1987, which pre-dated the NeXTSTEP dock (released in 1989). They are similar in how they can control an application, however, in practice their differences are extensive. The Iconbar holds icons which represent file systems, running applications, (optionally) minimized windows and a system-wide control utility named the Task manager. The application icons allow creation of new documents, application wide menu options such as preferences, and quit. Files (or anything on the desktop that can be saved) can be dragged to an application icon on the Iconbar to load the file as a new document, as opposed to merging/inserting the file in a current document. This will also override the current default application for that filetype. Also, the Mac OS X Dock will scale down accordingly to accommodate expansion, whereas the Iconbar will simply scroll. Furthermore, the Iconbar itself has a fixed size and position, which is across the bottom of the screen. While the Dock in Mac OS X can optionally be hidden, the Iconbar can be covered by overlaid windows. Both the Dock and Iconbar can be revealed (or surfaced) by moving the mouse pointer to the border of its location on screen.

Many programs which emulate the OS X dock on Windows, such as ObjectDock and RocketDock, have sprung up due to the popularity of Mac OS X. Earlier versions of Mac OS (before 10.0) did not have a dock, but an add-on such as A-dock adds a dock for users of earlier versions.

Various docks are also used in Linux and BSD. Some examples are Gnome Dock for GNOME, Kiba-Dock and Avant Window Navigator, which need a composite manager running and integrate best with Gnome, KXDocker (amongst others) for KDE and various other gdesklet/adesklets docks, AfterStep's Wharf (a direct derivation from the NeXTSTEP UI), gOS and Blackbox's Slit.

There has also been a dock in the Amiga Workbench since AmigaOS 3.x.

Mac OS X Dockling. Used to control an application without bringing it into focus

• Taskbar
• Gnome-panel
• Kicker (KDE)
• Avant Window Navigator