The Commodore 1571 is Commodore's high-end 5¼" floppy disk drive. With its double-sided drive mechanism, it has the ability to use double-sided, double-density (DS/DD) floppy disks natively. This is in contrast to its predecessors, the 1541 and 1570, which can fully read and write such disks only if the user manually flipped them over to access the second side. Because flipping the disk also reverses the direction of rotation, the two methods are not interchangeable; disks which had their back side created in a 1541 by flipping them over would have to be flipped in the 1571 too, and the back side of disks written in a 1571 using the native support for two-sided operation could not be read in a 1541
Source: Wikipedia, "Commodore 1571", available under the CC-BY-SA License.