.NET - ASP.NET AJAX

The MinimumPrefixLength property sets the minimum number of characters that must be entered before getting suggestions from the Web service.

Client-side libraries contain built-in code to make asynchronous calls over XMLHTTP. These libraries automatically handle browser compatibility issues. These libraries are based on a programming model similar to ASP.NET.

Yes, page methods and Web services are the two techniques to call the server-side code from JavaScript.

You can divide the ASP.NET AJAX architecture into two components - AJAX client architecture and AJAX server architecture.