You now know that compilers that target the .NET Framework produce managed modules and that managed modules contain CIL and metadata. But you might be surprised to learn that the CLR is incapable of using managed modules directly. That s because the fundamental unit of security versioning and deployment in the .NET Framework is not the managed module but the assembly.

An assembly is a collection of one or more files grouped together to form a logical unit. The term files in this context generally refers to managed modules but assemblies can include files that are not managed modules. Most assemblies contain just one file but assemblies can and sometimes do include multiple files. All the files that make up a multifile assembly must reside in the same directory. When you use the C# compiler to produce a simple EXE that EXE is not only a managed module it s an assembly. Most compilers are capable of producing managed modules that aren t assemblies and also of adding other files to the assemblies that they create. The .NET Framework SDK also includes a tool named AL (Assembly Linker) that joins files into assemblies.