How do pointers to virtual member functions work and why are they different than pointers to non-virtual member functions?

[JSolnit]

Hello, this is my first post to the C++ forum.

I have been asked by a potential employer to become an expert on all things relating to virtual functions and one specific aspect I was asked to look into was the difference between pointers to virtual and non-virtual member functions.

The information I've found thus far has been very light on explanation of the distinction. I know there's a size difference in memory, but I'm looking for a good explanation of what is different about the implementation of the two pointer types and why the pointer to a virtual member function requires more space.

Thanks for any insight you can provide.

[Cubbi]

The Fast Delegates article is a good place to start http://www.codeproject.com/Articles/7150/Member-Function-Pointers-and-the-Fastest-Possible