Since the dawn of PC graphical user interfaces (GUIs), operating system designers have struggled with window management: How users deal with the open applications, applets, dialog boxes, and other windows that typify such interfaces. Over time, as multitasking became more common, users would often leave open windows unattended for long periods of time. So Microsoft introduced the concept of "minimizing" windows that wouldn't be needed for a while. In Windows 3.x, minimized windows appeared as icons on the desktop.
With Windows 95, Microsoft added the system Taskbar, a thin pane running along the bottom of the screen that contains buttons representing most of the open windows the user is currently managing. Since then, the taskbar has been used to help the user, literally, switch tasks by clicking on buttons. (Advanced users are also familiar with the keyboard shortcut ALT+TAB, which accomplishes the same thing, and also allows you to easily switch to those windows that do not appear on the Taskbar.)
In its Windows 95 documentation, Microsoft says that it designed the taskbar to "make switching among multiple applications as simple as changing channels on a television set ... switching applications is a simple matter of selecting the desired 'channel' on the Taskbar ... the Taskbar [is] the TV Guide of Windows 95."
The primary goal of the original Taskbar was discoverability. Back in Windows 3.x, users would often switch to new applications or minimize existing windows and it was never clear where the window "went" in such cases. In Windows 95 and more recent Windows versions, when a user minimizes an application window, an animated minimize effect helps demonstrate where the window can be located in the future. That visual cue helped users become comfortable with the Taskbar.
The Windows 95 taskbar had a few basic additional features. The Taskbar buttons would resize automatically as more buttons were added to the Taskbar. It could be resized and moved to any edge of the screen. And you could auto-hide the Taskbar, so that it remained hidden unless you moused-over the screen edge in which it resided. Taskbar buttons could also be right-clicked to expose simple options.
Since then, the Taskbar has become a universal and expected part of the Windows user interface, and it's been augmented over the years to include various new features. The most notable change occurred in Windows XP, in 2001, when the Taskbar was augmented to allow button grouping. This feature addressed the issue that occurs when users were running more and more applications simultaneously, and certain applications, like Internet Explorer, often had multiple instances open, each with its own taskbar button. In XP, application group multiple Taskbar buttons by default, so you can click the button and access individual windows from a pop-up menu (Figure).
In Windows Vista, the Taskbar has been upgraded significantly again. In addition to the translucent glass effects provided by Windows, the Vista Taskbar has been upgraded with a new feature called Live Taskbar Thumbnails, which are designed to eliminate the confusion that arises when you have multiple windows open onscreen. With Live Taskbar Thumbnails, you can now mouse-over the individual Taskbar buttons for minimized or open windows and see a live preview of the underlying application window. The theory is that this will help users more quickly find exactly the window they're looking for. Here's what it looks like.
But what happens when you have enough windows open from the same application? If you mouse over a grouped Taskbar button, you won't see a preview. However, open the pop-up menu for that application button, and you'll be able to mouse over each button in the list and--voila!--you'll see a Live Thumbnail for each button there as well:
Tip: Live Taskbar Thumbnails offer some fun surprises. For example, if you have a video or visualization playing in Windows Media Player, you will see that video or visualization playing in real time in Media Player's Live Thumbnail. Videos also continue playing in Live Thumbnails if you minimize Media Player, though visualizations will appear paused even though they are still playing in the background.
Tip: If you don't like Live Thumbnails or find that they bog down your low-end PC, you can turn the feature off (just as you can turn off Taskbar Grouping as well). To do so, right-click on an empty area of the Taskbar and choose Properties. Then, uncheck the option titled Show window previews (thumbnails). When you do so, you'll get the old-style balloon help previews, as in Windows XP and before.