Theyhave key notches in different places. Among the pins is a notch. Looking from the top side, the notch on the DDR2 lies slightly to the right of the middle point of the memory stick. On the DDR3, the notch is slightly to the left of the middle. :Desktop_DDR_Memory_Comparison.svg
Thank you all. Found that ddr1 has written 184 at the end of the pin. 240 is written in ddr2 and ddr3. The way to differentiate ddr2 from ddr3 is the position of notches with ddr2 around the middle and ddr3 with notch more towards one end.
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