Color 4GB Kit 6400U Small Board. DDR is the first generation RAM, DDR2 is the second generation RAM, DDR3 is the third generation RAM. For example there are 1066MHz, 1333MHz and 1600MHz of DDR3 RAM, DDR3 1600MHz can underclocking work with motherboard which supports DDR3 1066MHz or DDR3 1333MHz.
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