"(The spelling disk and disc are used interchangeably except where trademarks preclude one usage, e.g. the Compact Disc logo. The choice of a particular form is frequently historical, as in IBM's usage of the disk form beginning in 1956 with the "IBM 350 disk storage unit").":
Laser disc, compact disc, digital video disc, and blu-ray disc are (from what I understand) officially spelled with the c. I'm in the US and that is the typical way to spell it that I see, but I also see the k is generally used for hard disk and floppy disk.
That said, there are a lot more instances of "disk" than "disc" used in the comments here so far.
> In 1979, the Dutch company Philips, along with Sony, developed and trademarked the compact disc using the "c" spelling. The "c" spelling is now used consistently for optical media such as the compact disc and similar technologies.
