I'm still a little confused on how the fusion drive works. I know the two are as one volume, and that the software manages everything itself, but what does that really mean? Are the OS and the applications permanantly stored on the SSD? Or is it really moving things back and forth from the hard drive everytime you use something more than another? I can't see the OS/apps exceeding 128GB, so it would make sense for them to all stay permanantly stored on the ssd, but is that the case?