In contrast, the Commodore 1581 3½" drive only supported 800 kB double-sided, double-density disks.
It also provided a "1541 emulation mode", allowing partitions on a 3½" disk to simulate the behavior of a 5¼" Commodore 1541 floppy.
The ability to use partitions and subdirectories was also expanded beyond the rudimentary form found in the 1581.
Sector 5 is the Device Information Block, which is $FF filled except in a few specific places.
Header Contents The BAM (Block Allocation Map) starts at 1/2 (track 1, sector 2) and continues to 1/33.