Windows Sidebar

Windows Sidebar is a component of Microsoft Windows. It allows to place multiple gadgets that could show information such as time, weather, calendar, and system resources use in a vertical bar at one side of the desktop, as well as other downloadable ones. It was first introduced in Windows Longhorn build 3683 as an addition to  and was last seen in early builds of Windows 7 before being replaced by a similar tool.

Pre-reset Windows Longhorn
Windows Sidebar was one of the features introduced in Windows Longhorn, and build 3683 is the earliest to contain it. While it's disabled by default, it can be enabled from the Taskbar and Start Menu Properties menu. Its default position is the desktop's right side, but it could be moved also to the left side. It could also be combined with the taskbar, a feature that made it disappear while its items were moved to the Sidebar. Although there are no tiles pinned at first, they can be easily added from the context menu's "Add a Tile" option. As development progressed, more changes were introduced, such as a new taskbar with the Sidebar integrated to it, new or changed tiles, and appearance retouches.

For most of the development, the Sidebar used the Plex-like blue and the light gray from the Windows Classic theme as its only color schemes. However, with the arrival of Milestone 7 build 4042 (Lab06_n) and the Slate theme in replacement of Plex, the Sidebar was updated to reflect this change, featuring now a darker gray as its predominant color. When the Jade theme was introduced later in build 4074, the Sidebar had the same color scheme as Slate's by default, but if Aero is enabled, a transparent black like Jade's will be used instead.

On several builds, particularly after build 4015,  is very unstable and often causes memory leaks. This is often because of the Sidebar which runs on it, meaning that it must be disabled to reduce their effects. While this problem disappeared for some time, chances of experiencing Explorer problems in general increased again with final builds such as those from the 408x line and build 4093.

Post-reset Windows Vista
Early builds compiled after the development reset of Longhorn had a more similar functionality to Windows XP, and thus didn't have any feature from the pre-reset project implemented yet. While Beta 1 builds already contained some Longhorn features, the Sidebar wasn't still present, and the earliest leaked build to contain it was Beta 2 build 5212 (winmain). This time, the Sidebar was running on its own process,, instead of  , a change that was intended to reduce memory leaks and instabilities from the Longhorn project. This Sidebar also lost some of its previous capabilities, such as being combined with the taskbar, and most of its previous tiles, which by this point had been renamed as gadgets. In build 5342, some additional tiles were added, but none of them were from Longhorn.

Since the first build, the Sidebar had a design reminiscent from late builds of Longhorn, being a transparent black bar, although the color's opacity was decreased in this case. In later builds, the black color was removed, leaving a fully transparent bar that now only appeared when the cursor was placed over the Sidebar's area. Otherwise, a dark shadow would appear on its place.

Replacement
While the Sidebar was from a few changes that survived to the Longhorn development reset, it was quickly replaced in Windows 7 build 6519 with Desktop Gadget Gallery, a similar feature that allowed gadgets to be placed anywhere on the desktop, rather than just on a bar, and gave them independent customization options. Desktop Gadget Gallery, however, would run the same fate as Windows Sidebar later since it was discontinued in Windows 8 due to security risks.