In computing, the taskbar is a term for an application desktop bar which is used to launch and monitor applications. Microsoft incorporated a taskbar in Windows 95 and it has been a defining aspect of Microsoft Windows's graphical user interface ever since. Other desktop environments, such as KDE and GNOME also include a taskbar. Non-Windows platforms may use different terminology, such as Panel or Dock.
In Microsoft Windows, the default location for the taskbar is at the bottom of the screen, and from left to right it contains by default the Start menu button, Quick Launch bar, taskbar buttons and notification area. This has changed in pre-beta versions of the forthcoming Windows 7, which combines the Quick Launch bar and taskbar buttons and introduces Jump Lists.
The taskbar was originally developed as a feature of Windows 95, but it was based on a similar user interface feature called the tray that was developed as part of Microsoft's Cairo project. 
With the release of Windows XP, Microsoft changed the behavior of the taskbar to take advantage of Fitts' law.
- The Start menu, which is accessed by a button on the taskbar, contains commands that can access programs, documents, and settings.
- The Quick Launch bar, introduced with Internet Explorer 4, contains shortcuts to applications. Windows provides default entries, such as Internet Explorer, and the user or third-party software may add any further shortcuts that they choose. A single click on the application's icon in this area launches the application. This section may not always be present: for example it is turned off by default in Windows XP Home Edition, although it can be enabled. In Windows 7 the Quick Launch has been merged with the taskbar buttons.
- The Windows shell places a taskbar button on the taskbar whenever an application creates an unowned window: that is, a window that doesn't have a parent and that is created according to normal Windows user interface guidelines. Typically all Single Document Interface applications have a single taskbar button for each open window, although modal windows may also appear there.
- Windows XP introduced taskbar grouping, which can group the taskbar buttons of several windows from the same application into a single button. This button pops up a menu listing all the grouped windows when clicked. This keeps the taskbar from being overcrowded when many windows are open at once.
- Windows Vista introduced window previews which show thumbnail views of the application in real-time. This capability is provided by the Desktop Window Manager.
- Pre-beta versions of Windows 7 introduce jumplists. Jumplists are menus that provide shortcuts to recently opened documents, or various options which apply to that specific program, that appear when the user right-clicks on an icon in the taskbar.
- Deskbands are minimized functional, long-running programs, such as Windows Media Player. Programs that minimize to deskbands aren't displayed in the taskbar.
- The notification area is the portion of the taskbar that displays icons for system and program features that have no presence on the desktop as well as the time and the volume icon. It contains mainly icons that show status information, though some programs, such as Winamp, use it for minimized windows. By default, this is located in the bottom-right of the primary monitor (or bottom-left on languages of Windows that use right-to-left reading order), or at the bottom of the taskbar if docked vertically. The clock appears here, and applications can put icons in the notification area to indicate the status of an operation or to notify the user about an event. For example, an application might put a printer icon in the status area to show that a print job is under way, or a display driver application may provide quick access to various screen resolutions. The notification area is commonly referred to as the system tray, which Microsoft states is wrong,  though the term is used at times in Microsoft documentation,   articles, and software descriptions. Raymond Chen suggests the confusion originated with systray.exe, a small application that controlled some icons within the notification area in Windows 95.
- Starting with Windows XP, the user can choose to always show or hide some icons, or hide them if inactive for some time. A button allows the user to reveal all the icons.
- Starting with Windows Vista, the taskbar notification area is split into two areas; one reserved for system icons including clock, volume, network and power. The other is for applications.
The Windows taskbar can be modified by users in several ways. The position of the taskbar can be changed to appear on any edge of the primary display. Up to and including Windows Server 2008, the taskbar is constrained to single display, although third-party utilities such as UltraMon allow it to span multiple displays. When the taskbar is displayed vertically on versions of Windows prior to Windows Vista, the Start menu button will only display the text "Start" or translated equivalent if the taskbar is wide enough to show the full text. However, the edge of the taskbar (in any position) can be dragged to control its height (width for a vertical taskbar); this is especially useful for a vertical taskbar to show window titles next to the window icons.
Users can resize the height (or width when displayed vertically) of the taskbar up to half of the display area. To avoid inadverdent resizing or repositioning of the taskbar, Windows XP Home Edition locks the taskbar by default.  When unlocked, "grips" are displayed next to the movable elements which allow grabbing with the mouse to move and size. These grips slightly decrease amount of available space in the taskbar.
The taskbar as a whole can be hidden until it the mouse pointer is moved to the display edge, or has keyboard focus.
Other toolbars, known as "Deskbands", may be added to the taskbar. Windows includes the following deskbands but does not display them by default (except the Quick Launch toolbar in certain versions and configurations).
- Address. Contains an address bar similar to what is found in Internet Explorer.
- Windows Media Player. Optionally shown when the Windows Media Player is minimized.
- Links. Shortcuts to items located in the users Links folder. Usually shortcuts to internet sites.
- Tablet PC Input Panel. Contains a button to show the Tablet PC input panel for ink text entry.
- Desktop. Contains shortcuts to items contained on the users desktop. Since the taskbar is always shown, this provides easy access to desktop items without having to minimize applications.
- Quick Launch. Contains shortcuts to Internet Explorer, email applications and a link to display the desktop. Windows Vista adds a link to the Flip 3D feature and Snipping tool.
- Language. Contains shortcuts to quickly change the desired language for the keyboard to follow.
In addition to deskbands, Windows supports "Application Desktop Toolbars" (also called "appbands") that supports creating additional toolbars that can dock to any side of the screen, and cannot be overlaid by other applications.
Users can add additional toolbars that display the contents of folders. The display for toolbars that represent folder items (such as Links, Desktop and Quick Launch) can be changed to show large icons and the text for each item. Prior to Windows Vista, the Desktop Toolbars could be dragged off the taskbar and float independently, or docked to a display edge. Windows Vista greatly limited, but did not eliminate the ability to have desktop toolbar not attached to the taskbar .
- Upon opening the Taskbar properties on Windows 95 and Windows 98 whilst holding down the CTRL key, an extra tab for DeskBar Options is shown, but no part of it can be used. The DeskBar option was a feature that never got included within these versions of Windows .
Other desktop environments
An early implementation of the taskbar concept is seen in Acorn Computers Arthur operating system, which was released in 1987 for their Acorn Archimedes computer. It is called the Iconbar and remains an essential part of Arthur's succeeding RISC OS operating system. The Iconbar holds icons which represent mounted disc drives and RAM discs, running applications and system utilities. These icons have their own context-sensitive menus and support drag and drop behaviour.
Unix and Unix-like
In various KDE distributions, the taskbar is run by the Kicker program, which shows rectangular panels that can contain applets, one of which is the taskbar. Applets can be arbitrarily relocated, for instance, the notification area can be moved away from the taskbar. The bar can be placed not only at the bottom, but also at the top or (vertically) at the left or the right and its size can be altered (from 24 to 256 pixels), as well as the length in % of the screen size. And several other bars with various specific functions can be added in different locations, eg, one bar at the left and one at the right or even overlapping (one fixed and one with automatic hiding).Since KDE4, the taskbar is implemented as a plasmoid.
Similarly, the GNOME desktop environment uses its own type of taskbar, known as panels (the program responsible for them is therefore called gnome-panel). By default, GNOME usually contains two full-width panels at the top and bottom of the screen. The top panel usually contains navigation menus labelled Applications, Places, and System in that order. These menus hold links to common applications, areas of the file system, and system preferences and administration utilities, respectively. The top panel usually contains a clock and notification area, which can double as a sort of dock, as well.The bottom panel is commonly empty by default, other than a set of buttons to navigate between desktops and a button to minimize all windows and show the desktop, due to its use in the navigation between windows (windows minimize to the bottom panel by default).
These panels can be populated with other customizable menus and buttons, including new menus, search boxes, and icons to perform quick-launch like functions. Other applications can also be attached to the panels, and the contents of the panels can be moved, removed, or configured in other ways.
Other Unix environments
There are many programs that offer standalone taskbars for desktop environments or window managers without one. Example include pypanel, fbpanel, perlpanel, and others.
Apple Macintosh computers
The Dock, as featured in Mac OS X and its predecessor NEXTSTEP, is also a kind of taskbar. The Mac OS X Dock is application-oriented instead of window-oriented. Each running application is represented by one icon in the Dock regardless of how many windows it has on screen. A textual menu can be opened by right-clicking on the dock icon that gives access to an application's windows, among other functions determined by the app. Minimized windows also appear in the dock, in the rightmost section, represented by a graphical thumbnail. The trash can is also represented in the Dock, as a universal metaphor for deletion. For example, dragging selected text to the trash should remove the text from the document and create a clipping file in the trash.
Notes and References
- Web site: The Windows 95 User Interface: A Case Study in Usability Engineering. Kent Sullivan. April 17, 1996. CHI 96 Design Briefs. 2008-10-22.
- Web site: Why do some people call the taskbar the "tray"?. Chen. Raymond. Raymond Chen. September 10, 2003. 2008-04-20. The Old New Thing. Microsoft.
- Web site: Giving You Fitts. Harris. Jensen. August 22, 2006. 2008-01-14. Jensen Harris: An Office User Interface Blog. Microsoft.
- Web site: Differences with Windows XP Home Edition. November 3, 2005. 2008-04-20. Windows XP Resource Kit. Microsoft.
- http://msdn.microsoft.com/en-us/library/aa511448.aspx Windows Vista Developer Center - The Windows desktop
- Web site: How to remove items from the notification area in Windows 2000. November 1, 2006. 2008-10-21.
- Web site: http://msdn.microsoft.com/en-us/library/aa511448.aspx. Microsoft Developer Network.
- Web site: How To Manipulate Icons in the System Tray with Visual Basic. 2004-07-15. 2009-01-23.
- Web site: How to use the System Tray directly from Visual Basic. 2006-09-26. 2009-01-23.
- Web site: System Tray Icon Sample. 2009-01-23.
- Web site: System Tray Balloon Tips and Freeing Resources Quickly in .NET. 2002-11. 2009-01-23.
- Web site: Microsoft Time Zone. 2004-10-20. 2009-01-23.
- Web site: When I dock my taskbar vertically, why does the word "Start" disappear?. Chen. Raymond. Raymond Chen. September 20, 2003. 2008-04-20. The Old New Thing. Microsoft.
- Web site: Cannot Move or Resize the Taskbar or Any Toolbars on the Taskbar (MSKB279774). January 25, 2006. 2008-04-20. Knowledge Base. Microsoft.
- Web site: Notification Area. Windows Vista User Experience Guidelines. Microsoft.
- Web site: Using Application Desktop Toolbars. Microsoft.
- http://windowshelp.microsoft.com/Windows/en-US/Help/5cca95d3-219a-436b-b016-831296b821ad1033.mspx Create a shortcut toolbar on the desktop
- http://support.microsoft.com/?id=226111 DeskBar Options Tab in Taskbar Properties Is Not Functional