The Common Language Specification (CLS) and the Common Type System (CTS), fundamental parts of the CLR, define the types and syntax that can be used with many .NET languages. The CTS is a standard that defines how CLR represents and manages types. The CLS is a subset of the features that programming languages must support in order to execute in the context of CLR.
The code that executes under control of CLR, such as C#, is called managed code, while the code that executes without requiring CLR, such as C++, is called unmanaged code. Prior to Visual Studio .NET 2002, all applications used unmanaged code. Applications such as MFC, ATL, and Win32 are unmanaged applications. When you are using managed code, the .NET Framework handles any interaction with the operating system, and you just concentrate on the application itself.
