You should not use AJAX if:

             =>  You want the page to show in a search engine, such as Google, because WebCrawler does not execute JavaScript code.

             =>  The browser does not support JavaScript.

             =>  You want to create a secure application.

The following validation controls are available in ASP.NET AJAX 4.0:

        => FilteredTextBoxExtender - Enables you to apply filtering to a text box.

        => MaskedEditExtender and MaskedEditValidator - Restricts a user to enter only a certain pattern of characters in the TextBox by applying a mask to the input.

        => ValidatorCalloutExtender - Attaches to the ASP.NET validators so that the error messages are not displayed as a simple text but as a balloon-style ToolTip.

        => NoBot - Prevents the spam/bot from filling the input forms automatically and uses the Completely Automated Public Turing test to tell Computers and Humans Apart (CAPTCHA), which is a type of challenge-response test to ensure that the response is not generated by the computer.

        => PasswordStrengthExtender - Measures the strength of the password text entered within the text box by validating with the different strength specified parameters

AJAX uses four technologies, which are as follows:

       => JavaScript

       => XMLHttpRequest

       => Document Object Model (DOM)

       => Extensible HTML (XHTML) and Cascading Style Sheets (CSS)

The ServiceInstaller class, also known as the project installer class, is used to install a Windows service.

The System.xml.dll is the real physical file, which contains the XML implementation. Some of the other namespaces that allow .NET to use XML are as follows:

      =>  System.Xml

      =>  System.Xml.Schema

      =>  System.Xml.XPath

      => System.Xml.Xsl

The different implementations of LINQ are:

      =>  LINQ to SQL - Refers to a component of.NET Framework version 3.5 that    provides a run-time infrastructure to manage relational data as objects.

      =>   LINQ to DataSet - Refers to a component that makes it easier and faster to query over data cached in a DataSet object.

      =>   LINQ to XML - Provides an in-memory XML programming interface.

      =>  LINQ to Objects - Refers to the use of LINQ queries with any IEnumerable or IEnumerable(T) collection directly, without the use of an intermediate LINQ provider or API, such as LINQ to SQL or LINQ to XML.

The standard query operators implement the IEnumerable<T> or the IQueryable<T> interface in C# and the IEnumerable(Of T) or the IQueryable(Of T) interface in Visual Basic.

The standard query operators in LINQ are the extension methods that form the LINQ pattern. These operators form an API that enables querying of any .NET array or collection. It operates on sequences and allows you to perform operations, such as determining if a value exists in the sequence and performing an aggregated function, such as a summation over a sequence.