'Retrieves the device containing the file.  The inode number and device
number together uniquely identify the file, but the device number is
not necessarily consistent across reboots or system crashes.
@raise NotImplementedError: if the platform is Windows, since the
device number would be 0 for all partitions on a Windows platform
@return: a number representing the device
@rtype: L{int}
@since: 11.0'

def getDevice(self):

    if platform.isWindows():
        raise NotImplementedError
    st = self._statinfo
    if (not st):
        self.restat()
        st = self._statinfo
    return st.st_dev
