The Framework Core

All applications created on the .NET development platform require two core pieces to run:

The Common Language Runtime (CLR) is a software engine that loads applications, verifies that they can execute without error, checks for the appropriate security permissions, executes applications, and cleans up after they are finished.

The .NET Framework class libraries provide developers with the software components that they need to write code that executes under the control of the CLR (known as managed code). They provide an enormous collection of functions—everything from file system and network access to XML functionality—in a single, logically organized hierarchy.

Together, the CLR and class libraries are often referred to as the “.NET Framework” and are included in Windows Server 2003 and Windows XP Service Pack 1, and can be installed on other versions of Windows.

Web server applications can also use ASP.NET, a class library explained in detail in the section “ASP.NET“. ASP.NET is not required for desktop applications.