The assembly is used by the CLR as the smallest unit for the following:
An assembly must contain a manifest, which tells the CLR what else is in the assembly. The other elements fall into the following three categories:
An assembly can be just one file. Figure 17.1 details the contents of a single-file assembly. Alternatively, the structure can be split across multiple files.
An assembly can have only one manifest section across all the files that make up the assembly. There is nothing stopping you, however, from having a resource section (or any of the other available section types, such as Metadata and MSIL code) in separate files that make up an assembly.