How does virtual base class works internally ? How the call to base methods resolved by compiler?

I understand virtual functions, but I am confused with virtual base classes and how it would work internally. Can someone please help?

class Base { };

Derived: virtual public Base { };

I do understand there is a single copy which is passed on to Derived classes.

• But can someone please explain how this works internally?
• How it will be similar or different to virtual functions ?

• And how the call to base methods will get resolved?

• What happens if the Derived class has virtual base class and a virtual function?

Thanks.