USB MU's are multipartitioned FATX (Most of which act as one logical parttition) that seem to coexist on Fat32 - (I suspect there's header info in there too) to my knowlege , Why they thought it was a good idea to give the cache it's own partition I will never be sure (Perhaps it's got something to do with the use-less slider option thingy you can 'manage' it with. I've had loads of probs with these new USBMU's If you have one in when you try to mount a drive on, oh let's say x360 commander (Not he only app btw) you might find you MU wiped!! It kept happening to me earlier and took me a while to figure-out what it was (I initialy blamed Freeboot and rebuilt it several times

) On the bright side though I have since figured-out how to have a 320gb USB HDD formatted as (16gb USBMU, 100gb NTFS and the rest FAT32 all on the one drive!!) I will let you all know how it goes (I'm sure it's only a matter of time before something happens and the bubble is burst on this one, but for now it's working
Brgds/Dan
All the xbox does is make a folder with the allocated space you picked using the slider split into chunks in it. The slider is so you can pick how much space you want to use on a HDD that already has data on it with out destroying that data. It makes a FATX Multi partition drive image, splits it into chunks to get around FAT32 file size limitations, and stores them in a folder on the USB drive. It's pretty much the only way they could do it with out making you have to reformat the device. I used a 2TB drive for a while that had 16GB reserved for the 360, the rest was FSD and all my games, and it worked fine. The only reason I stopped using it was I got a 250 gig HDD to put on the box and didn't need the 16gb on the 2TB anymore. Theres no reason you should run into problems.