-

Assemblies are the essential unit of deployment, version control, reuse, activation scoping, and security rights in.NET Framework applications. An assembly is a group of types and resources designed to work together as a logical unit of functionality. The information needed for the common language runtime to be aware of type implementations is provided via an assembly. Outside of the context of an assembly, a type does not exist to the runtime.

Assemblies are a fundamental part of programming with the .NET Framework. An assembly performs the following functions:

It contains code that is executed by the common language runtime. If a portable executable (PE) file does not have an associated assembly manifest, the code written in Microsoft intermediate language (MSIL) will not be executed. It's worth noting that each assembly can only have one access point (that is, DllMain, WinMain, or Main).

It forms a security boundary. An assembly is the unit at which permissions are requested and granted.
It forms a type boundary. Every type's identity includes the name of the assembly in which it resides. A type called MyType loaded in the scope of one assembly is not the same as a type called MyType loaded in the scope of another assembly.