In the BIOS, “Advanced->Chipset Configuration->North Bridge->DIMM Configuration->DDR Speed” settings allow user to run memory at different frequencies. In both “Auto” and “Force 1600” modes, where “Force 1600” cap the max freq at 1600MHz, memory speed was determined based on Intel’s POR, which dictated by processor type, DIMM frequency, memory rank, operating voltage, and memory population scheme in a complex matrix. And therefore the speed will not be essentially the same as the speed rating of the DIMM per Intel specs. In “Force SPD” mode, the system will force to use the DRAM’s speed for DDR speed in the BIOS. You can change the DDR Speed option to “Force SPD” to run memory at 1600MHz.