You can differ them, first by color, then the one with less dots in the slot is the sdram usually with 2 areas without holes and the one with only the interruption in the middle of the holes is the ddr-sdram.
i a thinking of upgrading my SD-RAM to DDR-RAM. my motherboard manual says it supports SD-RAM and DDR-RAM. how do i differ SD-RAM from DDR-RAM? do they use the same memory slots on the motherboard?