it will not run in dual channel active mode,just as two ram 2gb and 4gb,the lowest mhz ram will be ur ram speed,it will not double its mhz speed which is actualy dual channel mean.And if u want to run in dual channel u need to run same size ram in both slots,and lower mhz or speed ram will be ur system ram speed and if u use same mhz like 1333 both then it will be double in dual channel mode, and if u run one 1333 and another 1066 ur machine will be run on 1066 ram and dual channel it will be 2132 mhz actualy.