Please refer to the following URL to know the differences between CCW and RCW,http://onlydifferencefaqs.blogspot.in/2012/07/net-framework-difference-faqs-1_11.html

RCW ( Runtime  Callble Wrapper)  NET RUNTIME (CLR) is to communicate with COM RUNTIME , When .Net application is dependent on Com Component 

CCW (Com Callble Wrapper)   COM RUNTIME Object is to communicate with .NET RUN TTIME Object  (CLR)