JEDEC spec for DDR3 is 1066mhz. Due to it being official spec, many modules will default to that speed. Although a majority of the current performance memory out there is considerably faster, but will need to be set manually in BIOS. If you move memory out of the autodetected settings (recommended) set not only the Memory speed/Frequency but also the latency and voltage. A majority of all ram on the market will run at 1333 with little to no setup, 1600 usually requires settings to be specific, also in some cases *MAY* require a mild overclock to stabalize at that speed, unless you are running an extreem edition CPU.