That "drive" is most likely a recovery partition on your single drive, which shares the OS, DATA, and recovery data. DON'T use that partition for anything. If you are running out of space on your original drive, your best bet would be to buy a bigger drive and clone your existing to the new one.
An external usb hard drive can also be an ideal solution. I've used it to back up my files, then cleaned-up all the garbage from my computer.
Their portable, affordable and can easily be stored at a remote location if desired.