AJAX will revolutionize web development

Traditional web applications allow users to fill out forms, and when these forms are submitted, a request is sent to a web server. The web server acts upon whatever was sent by the form, and then responds back by sending a new web page. A lot of bandwidth is wasted since much of the HTML from the first page is present in the second page. Because a request to the web server has to be transmitted on every interaction with the application, the application's response time is dependent on the response time of the web server. This leads to user interfaces that are much slower than their native counterparts.
AJAX applications, on the other hand, can 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, and using JavaScript in the client to process the web server response. The result is more responsive applications, since the amount of data interchanged between the web browser and web server is vastly reduced. Web server processing time is also saved, since a lot of this is done on the computer from which the request came.
Image showing how a traditional web application handles user interaction comparing it to how an Ajax application handles it.
Image showing how the different components of Ajax applications interacts with each other comparing it to how traditional web applications do it.
A concrete example: Many sites use a table element to display tabular data. To change the sort order of the data with a traditional web application, the user would click on the table header which would send a request to the web server to reload the page with the new sort order. The web server would then construct a new SQL query with the new sort order, execute it and fetch the data from the database and reconstruct the web page and send it back to the user. Using AJAX technologies, this event could instead have been handled with a client-side JavaScript that dynamically generates a view of the tabular data with DHTML