Does SYNC have hard drive?

I was watching a Comcast on-demand "Searchlight" ad last night about the
2008 Focus.  It was said that SYNC copies your mp3 files to a "hard drive"
This is the only mention of a hard drive that I've heard of.  So do you
need to only allow SYNC to transfer your files the first time to a hard
drive in the car, then you don't need your mp3 player to play songs after
that?  Not that it's a big deal, as I intend to copy my music to a usb
thumb drive.

-Thanks