Microsoft's Windows Desktop Update was an optional feature included with Internet Explorer 4 (IE, released in September 1997), which introduced several updated shell features to the Windows 95 and Windows NT 4.0 operating systems. These features became part of the standard installation in Windows 98 and later versions.
The Windows Desktop Update included features such as Active Desktop and tight IE4 integration with the Windows Explorer. It was downloadable as part of IE4 for all versions of Windows 95 except Windows 95 OEM Service Release 2.5 (4.00.950C) which included a standalone version of IE 4.0 plus the Windows Desktop Update (but not slipstreamed) where it was automatically installed after the standard Windows 95 set-up. Similarly, the shell update was also made available as part of IE 4.0 for Windows NT 4.0 (with Service Pack 3 or later).
While the Windows Desktop Update was officially only an optional user component under Internet Explorer 4.0 releases, and was not formally included in any later version of Internet Explorer (IE5 onwards), users can extract the Windows Desktop Update installer from the IE4 setup files using standard .CAB extraction tools or use IEAK to generate a version of the IE 5.0x, 5.5 or 6.0 setup which included the update. Also command line parameters can be used to instruct installer of those versions of IE to install Desktop Update.
If the Windows Desktop Update was already installed, IE 5.0 or 5.5 setup installed some new shell features, such as sorting by name in a context menu and drop down/overflow menu buttons whenever menus or toolbar buttons did not fit in the Explorer window on the screen.
Updates to the Windows Desktop Update were part of IE 4.0 hotfixes and service packs. Later, shell security updates for Windows 95 and Windows NT 4.0 included both the update to the Windows Desktop Update version and the original version. Also sometimes the Windows Desktop Update version and the update to the original version were packaged separately.