And what can be done about it? I know that the i3-2100 cant be overclocked, but is there something wrong with my CPU? Or is there something can be done in the BIOS to increase the multiplier just a tad? Or does it only use half capacity when idle?
SB idles at 1.6ghz to save power, the instant your need more performance it'll go to full speed (if it was an i5/7 it has another load state[turbo]). This downclocking is called speedstep and first appeared in pentium 3s, of course now it's much more advanced and efficient to save power. You can disable it in bios but there's really no point unless you like to have a higher power consumption.