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. 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.

look of the dock
look of the dock

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 down) on the left, on the right, or default on the bottom edge of the screen.

the dock is on the left edge of the screen
the dock is on the left edge of the screen

the dock is on the right edge of the screen
the dock is on the right edge of the screen

the dock is on the bottom edge of the screen
the dock is 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.)

mouse over the dock element

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).

applications on the right part of the dock

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 dock tooltip