This 4GB RAM is 100% compatible with the ASRock C216 WS. What should be considered when upgrading RAM? It is possible to use different RAM sizes in the slots. The fast dual channel mode operation is optimally supported when the memory is installed in pairs. When mixing different memory sizes, the dual channel mode is activated in certain areas. For example, with a configuration of 4GB and 8GB, the Intel Flex technology would activate dual channel operation on the first 8GB.