What is AJAX?

AJAX is a relatively new Internet technology that grew out of combining JavaScript and XML. The term itself is an acronym for “Asynchronous JavaScript and XML.” The key feature of Ajax can be seen when the client requests new information. Instead of sending a whole new page, Ajax sends only the required new information. That means all of the buttons, text, graphics, and other objects that may be on a page do not have to be shipped over the Internet and reloaded into our browser.
ASP.NET 3.5 AJAX is easy to use and efficient. Using Visual Studio 2008, we can create an Ajax web site using only two Ajax controls. The main Ajax control is what is called the UpdatePanel, where all of the elements in our Ajax application can be placed. The other control is the ScriptManager. The ScriptManager control is required to access the Ajax Library and partial page rendering without post – back.