View source for Windows USER

{{Verifiability|date=March 2022}}
{{Short description|Component of Microsoft Windows}}
'''Windows USER''' is a component of the [[Microsoft Windows]] [[operating system]] that provides core functionality for building simple [[user interfaces]]. The component has existed in all versions of Windows, and includes functionality for [[Window manager|window management]], [[message passing]], [[Input device|input processing]] and standard [[GUI widget|controls]].

==Functionality and role==

Windows USER provides a large part of the core user experience for Microsoft Windows. Historically, it was responsible for:<ref name="petzold">Petzold, Charles (1998). ''Programming Windows Fifth Edition'', Microsoft Press,  {{ISBN|978-1-57231-995-0}} .</ref><ref name="chen">Chen, Raymond (2007). ''The Old New Thing'', Addison-Wesley Professional, {{ISBN|978-0-321-44030-3}} 
</ref>

* Causing windows to be drawn (using [[Graphics Device Interface|GDI]] as a device-independent API for drawing primitives)
* Obscuring [[stacking window manager|overlapping windows]] behind others
* Window size and positioning
* Providing all the standard window management controls (such as close boxes or [[title bar]]s)
* Providing the standard Windows [[menu bar]]
* Providing of standard controls (such as [[Button (computing)|button]], [[List box]] or [[Text box|Edit Box]])
* Providing [[Dialog manager|dialog box management]] (short-cut keys, tab key processing)
* Processing all user input from the mouse and keyboard
* The [[desktop metaphor|desktop]] background image (until [[Windows 8]])
* Drawing all standard visual elements
* [[Inter-process communication]] using [[Dynamic Data Exchange]]
* Mouse pointer cursor display and management
* Data transfer ([[Clipboard (software)|Clipboard]])

Gradually, as Windows has become larger and better factored, Windows USER has cooperated with other components to provide this functionality:

* Controls: Starting with [[Windows 95]], new controls were placed into a separate common controls component. Starting with [[Windows XP]], new implementations of the standard controls were also moved to that same component.{{Citation needed|date=January 2023}}
* Standard Visuals: Starting with Windows XP, visual elements are drawn by the Theming component.
* Windows Management experience: Starting with [[Windows Vista]], drawing standard window management was moved from Windows USER to the [[Desktop Window Manager]] when the [[Windows Aero|Aero]] theme is enabled. Starting with [[Windows 8]], window frames are always drawn by DWM, except in the [[Windows Preinstallation Environment]].
* Inter-program communication: Starting with Windows 3.1, [[Object Linking and Embedding]] replaced Dynamic Data Exchange as the recommended model for inter program communication.
* Menu bar: Starting in Windows 7, the [[Ribbon (computing)|Ribbon]] interface is a recommended replacement for the menu bar and context menus. It is provided by the UIRibbon component.<ref>[http://msdn.microsoft.com/en-us/library/dd371191(VS.85).aspx Windows Ribbon Framework]</ref>
* Desktop wallpaper: Starting in [[Windows 8]], drawing of the desktop wallpaper was moved to [[File Explorer|Windows Explorer]], except in the [[Windows Preinstallation Environment]], where the desktop wallpaper is drawn by the <code>WallpaperHost.exe</code> application. Wherever USER would have drawn the desktop background before, black is drawn, except when DWM is enabled, in which case, the user's accent will be drawn instead.{{Citation needed|date=January 2023}}
* Mouse pointer: Starting in [[Windows Vista]] when DWM is enabled, drawing of the mouse pointer is managed by it. However, starting in [[Windows 11]], it will no longer display with DWM disabled, unless the file <code>%SystemRoot%\System32\DWMInit.dll</code> does not exist.

==Developer experience==

Windows USER implements abstractions that are used to build Windows applications. These include

* <code>HWND</code> (Handle to Window)

The <code>HWND</code> is the basic unit of visual display and input in the Windows developer platform. All visual elements either have their own HWNDs or live as part of a larger <code>HWND</code>. Many functions in Windows USER manipulate properties on HWNDs such as size, position and title. Each <code>HWND</code> also has a communication channel (<code>WNDPROC</code> - Window Procedure) for delivery of messages.

Windows are managed as a tree, with the desktop window at the root of the hierarchy. Child windows are usually (but not always) visually contained within their parents.

* <code>MSG</code> (Message)

Applications and the operating system communicate with HWNDs using messages. A window message is the combination of a target <code>HWND</code>, a message code, and other details such as mouse position.

* Message Loop

By combining calls to Windows USER in the right way, a Windows application processes messages. The core Windows message loop (including calls to <code>GetMessage</code>, <code>TranslateMessage</code> and <code>DispatchMessage</code>) is at the core of any Windows application.

Developer functionality related to Windows USER is provided in the C header file winuser.h.

==Implementation==

In 16-bit versions of Windows, Windows USER was implemented as a file called user.exe. The file extension here was a [[misnomer]], as Windows USER was in fact always a [[dynamic link library]].

In 32-bit versions of Windows, the 32-bit version of Windows USER is called user32.dll and is located in the System32 directory, while compatibility with 16-bit applications is provided by having a modified version of user.exe also present.

In 64-bit versions of Windows, the 64-bit implementation of Windows USER is called user32.dll and is located in the System32 directory, while a modified 32-bit version (also called user32.dll) is present in the SysWOW64 directory.

==See also==
*[[Graphics Device Interface]] (GDI)
*[[Microsoft Windows library files]]

==References==
{{reflist}}

==External links==
*[http://csi-windows.com/blog/all/73-windows-64-bit/379-what-is-wow64-windows-64-bit Comprehensive Reference on WOW64 Folders, Variables, Values and References] {{Webarchive|url=https://web.archive.org/web/20140621053622/http://csi-windows.com/blog/all/73-windows-64-bit/379-what-is-wow64-windows-64-bit |date=2014-06-21 }}

{{Windows Components}}

[[Category:Windows NT architecture]]
[[Category:Windows components]]
[[Category:Windows technology]]