How big is an exabyte? One million terabytes. In 2007 the world’s total computer data was, compressed, 295 exabytes. How many hard-drives would it take to stores all that data? Assuming you get a large 2 tb hard-drive it would take 148 million! Now what if I told you you could store all that in less than one gram of DNA? Nature and Science both have reports of a paper, published in Science, that shows how DNA can be used to store data.