Hahvahd scientists have successfully stored 70 billion copies of their own book on genetics and biology in just a gram of DNA. That's 700 terabytes, in a gram.
DNA is a fantastic medium from a storage perspective. Its storage density is one million gigabits per cubic millimeter. A gigabit is a billion bits, and one gigabit equals 125 megabytes. So a million gigabits, if I'm not such a math idiot as some have said, is 125,000 gigabytes … in one cubic millimeter.
That's a little more storage than fits in your new MacBook Air.