Back in the 1980s floppy disks were expensive. And many early floppy disk drives were only single sided, which means they only had one read/write head and would only use one disk side. Both Commodore and Apple-II users quickly figured out that you could flip the disk around, if you punched a hole into the other side of the disk. This is a quick explanation on why this helped to double your disk capacity and some other differences between Commodore and IBM disk drives.