Xbox 360 hard drive: Really 20GB?

Source - Joystiq

Lucky Xbox 360 Premium owners may have noticed only 13GB of free space on their hard drives. That’s seven gigs shy of the advertised 20. What happend to all that space?

IGN writes: “The [BC] emulator is included in the HDD, along with some reserved space to download compatibility updates [and patches] for more games. Also, keep in mind that some content, like music videos and the puzzle game Hexic, is already preloaded on the HDD.”

Fortunately, users can delete content if they have to start making choices about hard drive space. But the system will always reserve space for backwards compatibility along with system patches and updates.

A larger amount of space would be better. I haven't got my Xbox360 yet, so I don't know if you could just put any harddrive in it. Otherwise a 100GB would be seriously cool! :D