Petabyte-class disk drives in five years?

For someone who has never seen these terms before: a Gigabyte is 1,024 Megabytes, a Terabyte is 1,024 Gigabytes, and a Petabyte is the next level up, equal to 1,024 Terabytes.

But just how big is that? A Petabyte hard drive is roughly equivalent to 2,097 hard drives of 500GB each. To put it another way, it could store approximately 170 million regular MP3 songs!