Although current homogeneous chips tightly couple the cores with cache-coherent shared virtual memory (CCSVM), this is not the communication paradigm used by any current heterogeneous chip. In this paper, we present a CCSVM design for a CPU/GPU chip, as well as an extension of the pthreads programming model for programming this HMC. We experimentally compare CCSVM/xthreads to a state-of-the-art CPU/GPU chip from AMD that runs OpenCL software. CCSVM's more efficient communication enables far better performance and far fewer DRAM accesses. © 2013 IEEE.