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This simple technique shows you how you would duplicate floppy disks in a GNU/Linux system using dd. This technique is not as useful as it used to be but can still be used for creating an image of a cd (although that is best done through the cd burning program).
This information has been taken from the Linux Online Classroom, see  in the Bibliography for further details.
$ dd if=/dev/fd0 of=floppy-image $ dd if=floppy-image of=/dev/fd0
The first dd makes an exact image of the floppy to the file floppy-image, the second one writes the image to the floppy. (The user has presumably switched the floppy before the second command. Otherwise the command pair is of doubtful usefulness).
Similar techinques can be used when creating bootdisks, you simply use dd to transfer the image to the floppy disk.