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

Take a good look at any project's References node. You'll never find mscorlib.dll listed there. It is special, any compiler needs it because it contains types that are required to make the language syntax work. System.Array, System.Int32, System.String, System.Exception, etc.

You can write a program that doesn't have a dependency on System.dll (although it would be hard) but you can't write one that doesn't depend on mscorlib.dll