Cool. For a paltry $5,011,830 I'd have enough storage for all my mp3s.
1,000,000,000 (or 1,073,741,824 if you use 2^10 as a base instead of 10^3).
http://en.wikipedia.org/wiki/Petabyte
Yes, just a little elaboration though:
The computer operates in binary, which is base 2. We as humans (usually) are in base 10 also known as decimal. That makes "kilo" have a value of 1024 instead of 1,000. Thats also why 40 GB hard drives only have 37.2. Because they have 40 billion bytes. But when you measure that in base 2, thats 37.2 GB.