is the common name for a keyboard shortcut that has been in Microsoft Windows since Windows 1.0 (1985). This shortcut switches between application-level windows without using the mouse; hence it was named Task Switcher (Flip in Windows Vista).
orders windows by most recently used; thus, repeated keystrokes will switch between the two most recent tasks. It can also be used alternate between a full-size window and the desktop. The window environment maintains a Z-order list of top-level windows (tasks) with the most recently used tasks at the front and the desktop at the bottom, so the most recently used tasks can be switched to the most quickly.
The keyboard combination has also been incorporated in other operating systems and desktop environments such as KDE, Xfce, and GNOME. iOS and macOS have similar functionality by pressing but that switches applications rather than windows.
Behavior The use of the modifier key in using differs from typical modifier key use in the following ways: There is a difference in behavior when the user releases and presses again vs. holding continuously while pressing repeatedly. Releasing has an immediate effect: it closes the task switcher and switches to the selected task.
There are many subtleties to the behavior of , and they have remained mostly unchanged over the years.
The behavior follows these rules: If there is more than one window, the task list appears as soon as is pressed while is being held down. The task list remains open until is released. moves the cursor forward in the list; moves it backward. or will autorepeat if held down (useful if there are many windows). With the initial press of or , the selection cursor starts on the window immediately following or immediately preceding the active one. If there are no topmost windows above the active window, an initial wraps the cursor around to the end of the list. Using the mouse to click on a task icon in the task window switches to that task (does not work on Windows XP and earlier). Pressing or clicking the mouse outside of the task window while is still down cancels the switch. The windows are listed by their Z-order. Any windows that are "always on top" are placed at the front of the Z-order sequence, followed by the current window and the windows underneath it. The desktop is given a window just like it was a top-level window. This no longer works on Windows 10. Switching to a window moves it to the front of the Z-order, with the exception that "always on top" windows remain topmost and at the front of the list. When the task switcher window is not active, places the active window at the bottom of the Z-order. In Windows 8 the behavior has changed: the window will be moved one level down the Z-order instead of going to the end. is equivalent to one except that minimized windows are selected without being restored. Minimizing a window also sends it to the back of the Z-order in the same way as .
The rules have the following consequences: In the absence of "always on top" windows such as Task Manager, pressing , pressing , releasing , and releasing (the typical way keyboard modifiers are used) will always alternate between the two most recent tasks. can restore the most recently minimized window. (If there are "always on top" windows, the lowest of these will be selected instead.) Pressing - (two tabs with continuously held down) performs the same quick switch back and forth, but between three programs. Any number of presses can be used to achieve this with any number of windows.
When the task list is initially activated by pressing , the list is populated in this order: Any 'always-on-top' top-level windows according to Z-order, front-to-back. All ordinary top-level windows according to Z-order, front-to-back.
The task list does not change order while it is open, but the order of tasks can change between invocations of the task list.
Windows Vista changed the default behavior (under most default installations) with its Flip interface. The six most recently used items in the Flip order work as described, then remaining windows are ordered alphabetically by application path (and optionally grouped, depending on the 'group similar taskbar buttons' setting which is enabled by default).
Windows 10 removed the desktop from the task list.
Illustrative examples
Windows may be divided into two categories, 'always-on-top' and ordinary. When a task is switched to, it is moved to the head of its category. For the following example, suppose there are no 'always-on-top' windows. Let A be the current window title. Hold down Alt and press and release Tab once, leaving Alt pressed. The window list comes up. A is guaranteed to be first in the list. Suppose the complete list is A W Z E U B C. The selection cursor will initially be on W. Suppose we want to switch to window U. Without releasing Alt, press Tab three more times and then release Alt. Then hold down Alt and press-release Tab once leaving Alt down. The window list will now show U A W Z E B C. Then Tab over to E and release Alt, selecting window E. Press and hold down Alt and press-release Tab once leaving Alt down. The window list will now show E U A W Z B C. Note that the windows switched to with (E, U, A) are in order of how recently they were switched to. Now Tab over to A and release Alt. Press and hold down Alt and press-release Tab leaving Alt down. The window list will show A E U W Z B C. The effect of this most-recently used behavior is that to return to the most recent task, Tab is pressed once, for the second most recent task Tab is pressed twice, and so on for all tasks. The priority of a window in terms of accessibility is how recently it was used. If A is now minimized, the list will become E U W Z B C A, and if Z is minimized the list becomes E U W B C A Z. Thus minimizing a window mimics the effect of not using it for a long time.
The commonplace alternation between the 2 most recent tasks (using a fast with all keys released immediately) is precisely a special case of the above behavior. Suppose the windows are A B C and we want to alternate between A and B. Hold Alt while pressing and releasing Tab; continue holding Alt. The list will show A B C and the cursor will initially be over B. When Alt is released B will be selected, Tab having been pressed a total of 1 time, and zero attention to the task selection cursor having been necessary. Again, press and release Tab while holding Alt. The list will show B A C and the cursor will initially be over A. When Alt is released we have switched back to A. Displaying the list again, the order has returned to A B C and this sequence can recur. On close inspection, in the course of typing and releasing both keys quickly, the task list window can be observed to flicker for a split second, so . If the user has been switching among 3 applications and wants to dispense with one of them by minimizing, one of the remaining ones will be on top immediately after minimizing, and ordinarily will alternate between the 2 remaining windows. If a program fails to move to the end of the list when minimized, pressing once will return to the minimized program. Failures such as this can result in a frenzied reordering of the list by means of several --... sequences to compensate for the program misbehavior. The algorithm for this reshuffling is intuitive after using for a long time. If the user attempts to switch to an application using but the application fails to update its place in the z-order (for example, if its window procedure is hung), then the next time is invoked, the task selection cursor may initially point unexpectedly far into the list of icons, just past the application in question, which will not have been moved to the head of the list.
Applications have some say in where they are located in the order. The list of windows is altered by the creation and destruction of windows, programmatic hiding, showing, raising, and lowering of windows, and alterations to the window z-order.
The order of the list corresponds directly to the z-order, once the windows have been sorted according to 'always-on-top' status. Alt-Shift-Esc is equivalent to one Alt-Shift-Tab except that minimized windows are selected without being displayed.
Windows-specific issues and hacks
works even if Windows Explorer is no longer running. On Windows NT 3.51 and prior, is managed by CSRSS (Client/Server Runtime Subsystem). On Windows NT 4.0 and later, it's handled by the kernel mode windowing system driver (win32k.sys). It works even when and (Task Manager) (which are managed by Winlogon) do not.
may be intercepted (or effectively disabled) by means of a low-level keyboard hook. Such a technique is used by applications such as the Virtual Network Computing (VNC) viewer to pass keystrokes to the remote desktop when the VNC window is active.
Under Windows XP, the Tweak UI PowerToy, can adjust the number of rows and columns in the task list window, or it can be adjusted via a registry edit. This is helpful if there are so many windows that the list would spill over into multiple pages.
Another Microsoft PowerToy, Replacement, is available for Windows XP that displays a screenshot of each application in the task list rather than just its icon, and allows the user to use the mouse to select the desired application. A more advanced version of this functionality, named Windows Flip, is built into Windows Vista.
A number of third-party tools, similar to Replacement, are also available that add additional functionality to .
Additionally, Windows Vista and Windows 7 allow the user to navigate through the menu using mouse or arrow keys.
When the Aero Glass theme is enabled, Windows Vista also offers a 3D view of the windows themselves that animates as the user cycles through it. The behaviour is very similar to and is accessed by holding down the key instead of while pressing . While this view is visible, windows can be selected and made active by clicking on them with the mouse, and the list can be scrolled forward or backward using the mouse scroll wheel.
If there is only one window on the system, Windows does not show a selector dialog at all when is pressed; the key sequence will simply restore or give focus to that window in case it is minimized or not focused. This means that under Windows 10, no longer functions as a way to switch out of a full-screen application, since the desktop is no longer a window.
If the user prefers the smaller XP icons over the larger Vista "thumbnail" icons, they can change the functionality by: Start → Computer Hit the "System Properties" button (on the Toolbar under the File | Edit toolbar) Select "Advanced System Settings" (under Tasks grouping in the left-hand column); this brings up the "System Properties" dialog box, which should show the "Advanced Tab". Hit the Settings Button under Performance. Uncheck the "Enable Desktop Composition" checkbox (the 3rd checkbox from the top in the Custom list box). Hit OK The user may also stop the Dwm.exe process via Windows' Task Manager.
In Windows 7 , after a one-second delay, displays the full-sized application window immediately each time the cursor position changes, hiding all other windows. This is a part of Aero Peek feature, new in Windows 7. This behavior can be disabled along with Aero Peek: Control Panel - Performance Information and Tools - Adjust visual effects - uncheck Enable Aero Peek.
Delay is adjustable by setting the LivePreview_ms value in HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Explorer\AltTab registry key.