Is the namespace System associated with a single DLL or does it include multiple modules?

The namespace System in C# is not tied to a single specific DLL. It can include types from multiple assemblies (DLLs).

For example, in .NET Framework and .NET Core, different parts of the System namespace are implemented in different assemblies, such as System.Runtime.dll, System.Collections.dll, and others.

This is done for modularity and load optimization, so applications can use only the components they need.

Therefore, a namespace is a logical grouping of types, not a physical correspondence to a single DLL.