We discuss the difference between a formal semantics of the C standard, and a formal semantics of an implementation of C that satisfies the C standard. In this context we extend the CompCert semantics with end-of-array pointers and the possibility to byte-wise copy objects. This is a first and necessary step towards proving that the CompCert semantics refines the formal version of the C standard that is being developed in the Formalin project in Nijmegen.