The Dock is a user interface feature in the NeXTSTEP, OPENSTEP, and Mac OS X computer operating systems, but the Dock's functionality was radically changed in Mac OS X.
In NeXTSTEP and OPENSTEP, the Dock is a repository to store frequently used programs. The icon for the Workspace Manager and the Recycler icons are always visible. Programs that are hidden are differentiated from programs that are not by the use of an ellipsis in the icons of nonrunning programs.
In Mac 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, but resizes them dynamically and uses magnification to clarify smaller resized items, unlike the dock in the NeXT operating systems, where the capacity of the Dock is fixed and dependent on the resolution the screen is set at. However, this may be an attempt to recover some Shelf functionality since Mac OS X has no effective Shelf technology carried from its NeXT heritage.
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