Notes:
AJAX applications send requests to the web server to retrieve only the data that is needed, usually using SOAP or some other XML-based web services dialect. On the client, JavaScript processes the web server response. The result is a more responsive interface, since the amount of data interchanged between the web browser and web server is vastly reduced. Web server processing time is also saved, since much of it is done on the client.
And that in turn means that web-based applications can now be made to work much more like desktop ones.
There are issues to tackle when building such pages. For instance, it becomes difficult to bookmark a particular state of application. Back button should now take care of going back to last state of page instead of last page.