DDR is like SDRAM beside the fact that it works with rising and falling edges of clock when it write or read data.
the easiest way to know is to open the computer and lookt at the DIMMS,
and see what is written on them.
ifyou want to detect it and it is n't in your pc, if its slot has three part it's sdram else it 's ddr, but in your bios of your mother board it shows you it's sdram or ddram