Additionally, the reason it lists "3.40 GHz 1.70GHz" is that the PC is at idle. 3.4 is the maximum rated speed but when the computer idles it automatically downclocks, so it shows the actual speed at the time as 1.7 GHz.
If the computer were running intensive software that puts the CPU at higher load it may report "3.40 GHz 3.40 GHz," indicating the CPU is at full speed. The first number is the rated speed and the second the actual speed at that moment.