What is XmlHttpRequest in Ajax?

It is an object in Javascript that allows the browser to communicate to a web server asynchronously without making a postback.

What is Ajax?

Asyncronous Javascript and XML – Ajax is a combination of client side technologies that sets up asynchronous communication between the user interface and the web server so that partial page rendering occur instead of complete page postbacks.

What are the disadvantages of AJAX?

The disadvantages are:
a)Ajax is not so friendly with search engine indexing because it uses Javascript for much part of its code. Search engines generally do not index Javascript present in web pages.
b)Dynamically created pages created by ajax does not support back button which takes the user to the previous pages.

What is Ajax? What is ASP.NET AJAX?

The term Ajax was coined by Jesse James Garrett and is a short form for “Asynchronous Javascript and XML”. Ajax represents a set of commonly used techniques, like HTML/XHTML, CSS, Document Object Model(DOM), XML/XSLT, Javascript and the XMLHttpRequest object, to create RIA’s (Rich Internet Applications).
Ajax gives the user, the ability to dynamically and asynchronously interact with a web server, without using a plug-in or without compromising on the user’s ability to interact with the page. This is possible due to an object found in browsers called the XMLHttpRequest object.

ASP.NET AJAX :-

‘ASP.NET AJAX’ is a terminology coined by Microsoft for ‘their’ implementation of AJAX, which is a set of extensions to ASP.NET. These components allow you to build rich AJAX enabled web applications, which consists of both server side and client side libraries.
Which is the current version of ASP.NET AJAX Control Toolkit?
As of this writing, the toolkit version is Version 1.0.20229 (if you (if you are targeting Framework 2.0, ASP.NET AJAX 1.0 and Visual Studio 2005) and Version 3.0.20229 (if targeting .NET Framework 3.5 and Visual Studio 2008).

Explain differences between the page execution lifecycle of an ASP.NET page and an ASP.NET AJAX page?

In an asynchronous model, all the server side events occur, as they do in a synchronous model. The Microsoft AJAX Library also raises client side events. However when the page is rendered, asynchronous postback renders only the contents of the update panel, where as in a synchronous postback, the entire page is recreated and sent back to the browser.

Can I use ASP.NET AJAX with any other technology apart from ASP.NET?

To answer this question, check out this example of using ASP.NET AJAX with PHP, to demonstrate running ASP.NET AJAX outside of ASP.NET. Client-Side ASP.NET AJAX framework can be used with PHP and Coldfusion.

What is ASP.NET MVC?

ASP.NET MVC is a free, fully supported, Microsoft product that enables developers to easily build great web applications. It provides total control over your HTML and URLs, enables rich AJAX integration, and facilitates test driven development.