C# in a Nutshell, Second Edition

The .NET Framework

The Microsoft .NET Framework consists of two elements: a runtime environment called the Common Language Runtime (CLR), and a class library called the Framework Class Library (FCL). The FCL is built on top of the CLR and provides services needed by modern applications.

While applications targeting the .NET Framework interact directly with the FCL, the CLR serves as the underlying engine. In order to understand the .NET Framework, one first must understand the role of the CLR.

The Common Language Runtime

The CLR is a modern runtime environment that manages the execution of user code, providing services such as JIT compilation, memory management, exception management, debugging and profiling support, and integrated security and permission management.

Essentially, the CLR represents the foundation of Microsoft’s computing platform for the next decade. However, it has been a long time in the making. Its origins can be traced back to early 1997, when products such as Microsoft Transaction Server (MTS) were starting to deliver on the promise of a more declarative, service-oriented programming model. This new model allowed developers to declaratively annotate their components at development time, and then rely on the services of a runtime (such as MTS) to hijack component activation and intercept method calls, transparently layering in additional services such as transactions, security, just-in-time (JIT) activation, and more. This need to augment COM type information ...