ASP.Net is a specification by Microsoft which is used to create web applications and web services. It is a part of ".Net framework". You can create ASP.Net applications in most of the .Net compatible languages like Visual Basic, C#, etc. ASP.Net provides much better performance than scripting languages.

ASP.NET Framework is a part of the .NET framework used to create a dynamic website, web application, and web services. It is a server-side technology that uses all .NET compatible languages such as C#, VB.NET, J#, etc. which are compiled to Microsoft Intermediate Language (MSIL)

Features of ASP.NET:

• It uses C# and VB.NET languages to build the website.
• It allows us to separate the HTML layout with server-side code.
• It allows us to make the same class name qualifying under a different namespace.
• ASP.NET pages are compiled, not interpreted.
• ASP.NET is a request processing engine. It takes an incoming request and passes it through its internal pipeline to an endpoint where a developer can attach code to process that request.

The main difference between ASP and ASP.Net is that ASP is interpreted, while ASP.Net is compiled. ASP uses VBScript, therefore when the ASP page is executed, it is interpreted. On the other hand, ASP.Net uses .Net languages like C# and VB.NET, which is compiled to Microsoft intermediate language.

IIS stands for Internet Information Services. It is created by Microsoft to provide Internet-based services to ASP.NET Web applications.

Following are the main usage of IIS:

• IIS is used to make your computer to work as a Web server and provides the functionality to develop and deploy Web applications on the server.
• IIS handles the request and response cycle on the Web server.
• IIS also offers the services of SMTP and FrontPage server extensions.
• The SMTP is used to send emails and use FrontPage server extensions to get the dynamic features of IIS, such as form handler.

ASP.Net is the next generation of ASP technology platform. It is superior to ASP in the following ways:

• Highly Scalable
• Compiled Code
• User Authentication
• Language Support
• Third party control
• Configuration and Deployment are easy.
• Object and Page caching
• Strict coding requirements

There are the following differences between these two :

Web Site

• On a website, you cannot add multiple projects.
• There is no project file (.csproj or .vbproj). All the files in a folder structure are automatically included on the site/
• .By default, compilation produces multiple assemblies.
• The website is easy to create and deploy.
• You can use different .NET languages on a single web site such as VB.NET pages and C# pages can be used on a single website.
• You can edit a single page/file after deployment recompilation is not required.
• Choose a website where one developer will responsible for creating and managing an entire website. Since decoupling is not possible on the website.
• You cannot establish dependencies on the website.

Web Application

• In a web application, you can add multiple projects.

• It has a Visual Studio project file (.csproj or .vbproj) stores information about the project like as the list of files that are included in the project, and any project-to-project references.
• By default, compilation of code files (excluding .aspx and .ascx files) produces a single assembly.

• It is easy to develop compared to the website.

• You cannot use different .NET languages in a Web Application such as C# and VB.NET both cannot be used in a web application.

• You cannot edit a single file. Recompilation is required.

• The right choice for enterprise environments where multiple developers work for creating, testing, and deployment. Different groups work on various components independently like one group work on the domain layer, other work on the UI layer hence, decoupling is possible here

• You can establish dependencies in a Web Application.

Both files are used to define configurations for your ASP.NET application. There are the following differences between these two configuration files.

Web.config

• The Web.config is used to define application-level settings.
• If any setting is not specified in Web.config it inherits from Machine.config by default
• Web.config is an XML-based configuration file for an ASP.NET application that includes the setting for Data Connection, Customizing Security, State Management, Memory Management, Error Handling, and much more.
• It is sometimes called an application and session level configuration file.
• You can have more than one Web.config file in your ASP.NET application.

Machine.config

• This file is at the highest level in the configuration hierarchy.
• You can find it at <WinDir>\Microsoft.NET\Framework\<version>\config\machine.config 
• Machine.config is used for defining server level settings.
• It defines the supported configuration file section and ASP.NET work process.
• It registers providers that can be used for advanced features such as profiles membership and role-based security.
• It is automatically installed while installing Visual Studio.NET.
• It is sometimes called a machine level configuration file.
• Only one Machine.config file can be at the machine level.