A Common Substrate for all Development - Page 4

The major components of the .NET framework are shown in the following diagram:

The framework starts all the way down at the memory management and component loading level, and goes all the way up to multiple ways of rendering user and program interfaces. In between, there are layers that provide just about any system-level capability that a developer would need.

At the base is the Common Language Runtime, often abbreviated to CLR. This is the heart of the .NET framework, the engine that drives key functionality. It includes, for example, a common system of data types. These common types, plus a standard interface convention, make cross-language inheritance possible. In addition to allocation and management of memory, the CLR also does reference counting for objects, and handles garbage collection.

The middle layer includes the next generation of standard system services such as ADO.NET and XML. These services are brought under the control of the framework, making them universally available and standardizing their usage across languages.

The top layer includes user and program interfaces. Windows Forms (often informally referred to as WinForms) are a new way to create standard Win32 desktop applications, based on the Windows Foundation Classes (WFC) produced for J++. Web Forms provide a powerful, forms-based UI for the web. Web Services, which are perhaps the most revolutionary, provide a mechanism for programs to communicate over the Internet using SOAP. Web Services provide an analog of COM and DCOM for object brokering and interfacing, but based on Internet technologies so that allowance is made for integration even with non-Microsoft platforms. Web Forms and Web Services, comprise the Internet interface portion of .NET, and are implemented through a section of the .NET Framework referred to as ASP.NET.

All of these are available to any language that is based on the .NET platform. For completeness, there is also a console interface that allows creation of character-based applications (not shown in the diagram).

The Common Language Runtime

Let's start with a definition. A runtime is an environment in which programs are executed. The Common Language Runtime is therefore the environment in which we run our .NET applications that have been compiled to a common language, namely Microsoft Intermediate Language (MSIL), often referred to simply as IL. Runtimes have been around even longer than DOS, but the Common Language Runtime (CLR) is as advanced over traditional runtimes as a light bulb is over a candle. Here's a quick diagrammatic summary of the major pieces of the CLR:

That small part in the middle, called Execution Support, contains most of the capabilities normally associated with a language runtime (such as the VBRUNxxx.DLL runtime used with Visual Basic). The rest is new, at least for Microsoft platforms.

Chapter 2 of this book will go into the Common Language Runtime in depth. However, since understanding the CLR is key to understanding the rest of .NET, here is a short introduction.

Avoiding Confusion – the Role of the .NET Enterprise Servers - Page 3
Introducing .NET
Key Design Goals - Page 5