What is it?
Ajax applications can have the kind of rich user interfaces normally associated with desktop applications. They are also more responsive, because instead of reloading the whole page when the user makes a change or a request, they exchange the minimum possible data with the server while the application remains available to the user.
While providing undoubted performance benefits, this violates a number of rules and safeguards -it "breaks" the back button which enables you to return to the unmodified page, and means the URL no longer identifies a single, unique state of a page.
ASP.net Ajax is supported by Visual Studio 2008, supplied as part of ASP.net 3.5, and can be downloaded for ASP.net 2.0.
Where did it originate?
ASP.net Ajax began with the codename Atlas. It was released as a separate download early in 2007, then included with .net Framework 3.5, released at the same time as Visual Studio 2008 at the end of last year.
What's it for?
ASP.net Ajax supports ASP.net-style server-side programming, client-side programming or a combination of both. Developers can add partial update functionality to existing applications by wrapping sections of their websites in the Ajax server control 'update panel', which enables the server controls to update without a post-back.
There are alternatives to Microsoft's Ajax offering for ASP.Net. Gaia Ajax Widgets for .net is a commercial library of Ajax modules, some of which are also available in open source form. Ajax.net Professional, a widely used, independently developed, free library for ASP.net which pre-dated Microsoft's support for Ajax, now appears to have been abandoned.
What makes it special?
How difficult is it to master?
What systems does it run on?
Rates of pay
ASP.net developers with Ajax £25,000 -£40,000.