Building Interactive User Interfaces with Microsoft ASP. ...
The ASP.NET AJAX UpdatePanel provides a quick and easy way to implement a snappier, AJAX-based user interface in an ASP.NET WebForm. In a nutshell, UpdatePanels allow page developers to refresh selected parts of the page (instead of refreshing the entire page). Typically, an UpdatePanel contains user interface elements that would normally trigger a full page postback - controls like Buttons or DropDownLists that have their <code>AutoPostBack</code> property set to True. Such controls, when placed inside an UpdatePanel, cause a partial page postback to occur. On a partial page postback only the contents of the UpdatePanel are refreshed, avoiding the "flash" of having the entire page reloaded. (For a more in-depth look at the UpdatePanel control, refer back to the
