Just so you know, the 512 is DDR which means it is double regualr RAM.
Seriously? First, Double Regular RAM couldn't possibly be the meaning of DDR. It just doesn't match. Second, if you've actually been around computers long enough to remember the bogus memory doublers from the early 90s, you should know better than to think that's what DDR was. Besides, who would ever sell something as 'double the size of 512MB'? You would just say 1024MB.
DDR means Double Data Rate. Data is transferred twice per clock, leading to... double the throughput. It has nothing to do with capacity. Spend a few seconds googling next time.
It is also more energy efficient.
Being DDR has nothing to do with being energy efficient. All new memory is DDR. New memory gets produced on a smaller process than old memory. Smaller processes require less driving voltage, thus drawing less amperage and wasting less energy as heat. The two are nothing more than unrelated features on the same hardware.