Understanding Assemblies

An assembly is the actual .dll file on your hard drive where the classes in the .NET Framework are stored. For example, all the classes contained in the ASP.NET Framework are located in an assembly named System.Web.dll.
Each class entry in the .NET Framework SDK documentation lists the assembly and namespace associated with the class. For example, if you look up the MessageQueue class in the documentation, you'll discover that this class is located in the System.Messaging namespace located in the System.Messaging.dll assembly.