Commodore Business Machines's "advanced" disk drive for the C128. It was the double-sided version of the Commodore 1570 disk drive but, unlike the 1570, worked quite well.
The 1571 supported "burst mode" loading when used on a C128 in native mode, which increased the transfer speed from 1541 speed to about three kilobytes per second (about a 10-fold increase). The 1571 could be told to emulate a 1541 for use with a C64 or 1541 disks.
Bugs in early releases of the 1571 ROM affected access to the second side of the disk.