2 gig USB hard drive.
Sony Pocket Bit Pro, 2GB USB Hard Drive
It says, right there, that you can push a button, and have it back up pre-selected folders and subfolders, which sounds like it needs drivers on the computer side. As long as it works as plain USB storage, that's not so bad…
2 gig is a decent amount of space – more than enough to take a few things home, or back up a few important documents (or, perhaps, those mission critical recent downloads).