What happens when you run out of space on your hard drive? Sure, you can start purging old files and unneeded programs, but that will only get you so far. The other option is to add a second drive, or simply replace it. Replacing an entire drive can be a lot of work, what with copying everything over, and getting your computer set back up the way you like it, and few laptops allow a second drive. Well, if you're a MacBook owner, there's a new option at your disposal.