Commodore 1581 disk
The Commodore 1581 disk is the native format of the 1581 disk drive, a 3.5" disk drive released by Commodore for its Commodore 64 and 128 computers.
The 1581 disk has 80 logical tracks with 40 logical sectors in each, totalling 3200 sectors, each of which held 256 bytes. This led to a total storage capacity of 800 kilobytes. The physical structure of the disk was abstracted away by the on-board logic, presenting sequentially-numbered logical tracks and sectors to the operating system.
The prototype Commodore 65 computer used this type of disk.
The low-level format was similar enough to the PC-DOS 720K format to allow software-based emulation and data transfer between the two platforms.