The REAL speed, or Front Side Bus (FSB) speed, is 333.333...MHz, but, as your memory is DDR, or Double Data Rate, the data it contains is accessed at 666.6666...MHz, rounded to 667MHz.
That's why it's branded as 667MHz.
The reasoning been that you are more interested in how fast you can access the data (effective speed) than how fast the bus is running (raw speed).
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Another, but remote, possibility could be that your TOP FSB is realy only 166.5MHz. In this case, it's a hard limitation imposed by the motherboard making.
Electro, May 2012
