A memory module includes a first memory device that includes first circuit nodes for communication with a memory controller and second circuit nodes for communication inside the memory module, a second memory device that includes first circuit nodes for communication with the memory controller and second circuit nodes for communication inside the memory module, and an internal data bus that couples the first memory device to the second memory device to carry data between the second circuit nodes of the first memory device and the second circuit nodes of the second memory device. When an internal read command is applied to the first memory device and an internal write command is applied to the second memory device, data is transferred from the first memory device to the second memory device through the internal data bus.