Telling DDR and DDR2 apart is difficult, because the differences are subtle. However, care must be taken because DDR2 will not work in DDR machines, and DDR won't work in DDR2 machines. To find out which you have:
|Select "About This Mac" in your Apple Menu.|
|DDR SDRAM means you have the
PowerMac G5 Original that runs DDR RAM.
|DDR2 SDRAM means you have the
PowerMac G5 Dual Core that runs DDR2 RAM.