All DDR, DDR2, and DDR3 memory is actually running at half the clock speed reported by the manufacturers. They double the clock speed for marketing reasons related to the fact that DDR means double data rate.
Its like this. You know how light waves like radio waves look like? kinda similar, ups and downs equally spaced. I tired to make a diagram but this forum poster screwed it up every time after I hit post reply.
This is how the clock frequency works too. Normally work is done on only the top or the bottom of these fluctuations (usually the top). For DDR technologies work is done on both sides of the clock, effectively making it as fast as something with double the clock frequency. The edges are technically called the rising and falling ends of each clock cycle.
Technically your modules are running at 1066MHz. The proper term would be 1066MT/s, meaning Mega (mega being used just like in mega bits per second) Transfers per second but that would have been more complex to explain than simply doubling the reported clock frequency even though the actual frequency stayed the same.
This technique for speed improvement (DDR) has benefits over doubling the actual clock frequency of the device.