CPU-Z reports the operating frequency of the DRAM. Since DDR (DOUBLE Data Rate) memory transfers data on both the rising and falling edges of the clock signal, the actual clock speed is half of the advertised effective speed. CPU-Z shows the actual clock speed.

For example, if your DDR3 memory is rated at 1600 MHz, CPU-Z will show 800 MHz, as the effective rate is 800 MHz × 2 = 1600 MHz.