CLR Architect Vance Morrison has been very busy working on the future of the CLR, especially as it relates to execution performance and the type system. Some of his latest work is present in the upcoming 4th version of the virtual machine that powers all things .NET, CLR 4, which ships with Visual Studio 2010. Vance has been on the CLR team since its inception. MSIL, the intermediate language produced by the compilers of all .NET languages, is primarily Vance’s doing.   Here, Vance guides us through some of the history of the CLR, a look inside the upcoming version and some insights into the future. One of the things that Vance is thinking about with respect to type inheritance is what he calls default interfaces: they are contractual, but with default implementation characteristics, as opposed to purely abstract as interfaces are today. So, a default(implementation) interface is capabe of changing without breaking the systems that implement it. Wait a minute, that' goes against the basic rules of interfaces in the OO world. Vance explains. Relax. Meet Vance, the face of MSIL. There's much of his thinking and code inside the CLR. Learn about some this here. Tune in. Enjoy.