The Common Language Runtime (CLR) is the foundation upon which the Microsoft .NET strategy is built. The CLR provides an execution environment that manages running code and provides services that make software development easier. In order to start running managed code in a process, the CLR must be loaded and initialized. The host is responsible for loading the CLR. Most hosts consist of both unmanaged and managed code.

·         The unmanaged code is responsible for loading the CLR into a process and converting the program into managed code.

·         The managed portion of the host is responsible for creating and managing the application domains.

There are mainly 2 reasons for hosts to have managed code and unmanaged code. The primary reason is a performance issue. There is a performance associated with calling a managed code from unmanaged code or vice versa. Hence, it is a better to call the unmanaged code and then go ahead with managed code (instead of transitioning from unmanaged host code to managed user code). It is also easy to implement/manage.

These are some of the hosts:

·         ASP.NET

·         Internet Explorer

·         Shell Executables

·         SQL Server 2005