mscorlib.dll & System.dll

Question

Why did MS originally make the decision to maintain these two separate core libs? Maybe they had some scalability issue in mind, but nowadays I never see an application, of

Answer 1

This is just a guess, but mscorlib.dll probably also has some C code that's important to the CLR runtime as well as being a .NET assembly, or some mixed-mode code. System.dll is probably all managed.