Kind of. <b>D</b>ouble <b>D</b>ata <b>R</b>ate RAM sends data at the opening and falling edge of each clock pulse, so if the RAM operated at 200Mhz it would act like one at 400Mhz. Technically your DDR400 operates at a real world frequency of 200Mhz, but acts like one at 400Mhz.
OK it's your choice:
You can have the boat, or you can have the Mystery Box!
...Hey wait a minute! A boat's a boat, but a Mystery Box could be anything. It could even be a boat