Which is correct, disc or disk?

Question

We use "disc" to describe any thing that appears flat and round. This includes CD's, DVD's, floppies, frizbees and hard discs. The word "disk" came with the PC in the '80's and seemed to want to set the computer disc apart from all other discs.

Answer 1

Disc is used for cd's, dvd's. Disk is used for hard disk, floppies.

Answer 2

It would be correct to use "disc" to refer to any instance of a thin  circular device, like a floppy disc, or a brake disc, or a disc in the back, or the Sun's disc ...

You may also use the word "disk" although it is not strictly correct.