Which is the way RAM DDR2 or DDR3

Many people still doubt it impression that I know that the RAM is DDR2 or DDR3 with which I first ¤ notice of the leg groove RAM If groove is approximately in the middle of the RAM indicates that the RAM as DDR2, but if the groove as a bottom minuscule to the direction or the direction of showing that the RAM DDR3 or another way is to look at the screen bar number if it is PC2-5400. and PC2-8500 DDR2, but it would be if the PC3-10666 or PC3-12800 will be DDR3.