What is .NET ?
It is a platform neutral framework.
Is a layer between the operating system and the programming language.
It supports many programming languages, including VB.NET, C# etc.
.NET provides a common set of class libraries, which can be accessed from any .NET based programming language. There will not be separate set of classes and libraries for each language. If you know any one .NET language, you can write code in any .NET language!!
In future versions of Windows, .NET will be freely distributed as part of operating system and users will never have to install .NET separately.What is Not ?
.NET is not an operating system.
.NET is not a programming language.".NET is a framework"Are you confused by this definition? Well, that is OK. It is really confusing!We cannot define .NET as a 'single thing'. It is a new, easy, and extensive programming platform. It is not a programming language, but it supports several programming languages. By default .NET comes with few programming languages including C# (C Sharp), VB.NET, J# and managed C++. .NET is a common platform for all the supported languages. It gives a common class library, which can be called from any of the supported languages. So, developers need not learn many libraries when they switch to a different language. Only the syntax is different for each language.When you write code in any language and compile, it will be converted to an 'Intermediate Language' (Microsoft Intermediate Language - MSIL). So, your compiled executable contains the IL and not really executable machine language. When the .NET application runs, the .NET framework in the target computer take care of the execution. (To run a .NET application, the target computer should have .NET framework installed.) The .NET framework converts the calls to .NET class libraries to the corresponding APIs of the Operating system.Whether you write code in C# or VB.NET, you are calling methods in the same .NET class libraries. The same .NET framework executes the C# and VB.NET applications. So, there won't be any performance difference based on the language you write code.What is Visual Studio.NET ?Many people always get confused with Visual Studio .NET (VS.NET) and .NET technology. VS.NET is just an editor, provided by Microsoft to help developers write .NET programs easily. VS.NET editor automatically generates lot of code, allows developers to drag and drop controls to a form, provide short cuts to compile and build the application etc.VS.NET is not a required thing to do .NET programming. You can simply use a notepad or any other simple editor to write your .NET code!!! And you can compile your .NET programs from the command prompt.Well, what I said is true theoretically.. but if you decide to use notepad for .NET programming, by the time you develop few sample applications, Microsoft would have introduced some other new technology and .NET would be outdated. You may not want that. So, let us go by VS.NET, just like every other .NET guys.