The Disk Drive, ComputerCraft, is an object that, when placed adjacently but not diagonally next to a computer, does the same as a disk drive for real computers in the real world would do: they allow the access to portable data storage devices (Floppy Disks).
2. Redstone Dust
To use a disk drive, place it adjacently but not diagonally next to a computer (left, right, top, bottom, front, or back side). Insert a disk by right-clicking on the disk drive and placing the disk in the slot above the inventory.
If you sneak and right click the disk drive with a disk/music disc in 1.4+ it will place it into it without needing to open the disk drives interface.
To play a music disk, you need to place the desired music disk in the drive, and then typing in the computer "dj".
If you want to edit on your Floppy Disk use "cd disk" and you are in your disk.
See Disk (API) for the disk API.