For those too lazy (or busy) to go and read it, the difference essentially boils down to this: "disc" refers to optical meda such as CD's and DVD's, and "disk" refers to magnetic media such as floppies and the hard drive in your computer...
If you're wondering how widespread that distinction is held, I checked, and Wikipedia concurs (in the technological realm anyway).
You learn something new every day, if you're open to it...
