Complex sentence: Apple DOS 3.1 disks use 13 sectors of data per track, each sector being 256 B. It uses 35 tracks per disk side, and can access only one side of the floppy disk, unless the user flipped the disk over.
Split into simpler sentences: Apple DOS 3.1 disks used 13 sectors of data per disk track, each sector being 256 B in size. It used 35 tracks per disk side, and could access only one side of the floppy disk, unless the user flipped the disk over.