4 Part I:The .NET Framework .NET is a collection of tools, technologies, and languages that all work  together in a framework to provide the solutions that are needed to easily build and d eploy truly robust enterprise applications. These .NET applications are also able to easily  communicate with one another and provide information and application logic, regardless of pla tforms and languages. Sounds pretty outstanding, doesn t it? Figure 1-1 shows an overview of the structure of the .NET Framework. Figure 1-1: The .NET Framework. The first thing that you should notice when looking at this diagram is t hat the .NET Framework sits on top of the operating system. Presently, the operating  systems that can take the .NET Framework include Windows XP, Windows 2000, and Windows NT. The re has also been a lot of talk about .NET being ported over by some third-party comp anies so that a majority of the .NET Framework could run on other platforms as well. NOTE: The support for the .NET Framework on Windows   NT is limited to functioning only as a client. Windows NT will not support the Framework as a server. At the base of the .NET Framework is the Common Language Runtime (CLR) . The CLR is the engine that manages the execution of the code. The next layer up is the .NET Framework Base Classes. This layer contains classes, value types, and interfaces that you will use often in your development proces s. Most notably within the .NET Framework Base Classes is ADO.NET, which provides access to and  management of data. The third layer of the framework is ASP.NET and Windows Forms. ASP.NET should not be viewed as the next version of Active Server Pages after ASP 3.0, but as  a dramatically new shift in Web application development. Using ASP.NET, it s now possibl e to build robust Web applications that are even more functional than Win32 applications of th e past. This was always quite difficult to do in the stateless nature of the Internet, bu t ASP.NET offers a number of different solutions to overcome the traditional limitations on  the types of applications that were possible. The ASP.NET section of the .NET Framewo rk is also where the XML Web services model resides.