Not many know that Microsoft originally invented AJAX. AJAX helps update data on a web page without a complete reload of the page.
ASP.NET AJAX was formerly known as Atlas. It is a set of extensions to ASP.NET developed by Microsoft for implementing Ajax functionality. ASP.NET AJAX was released as a standalone extension to ASP.NET in January 2007. It was subsequently included with .NET 3.5.
The key technology in ASP.NET AJAX is the XMLHttpRequest object, along with Javascript and DHTML.