Isn't language AMAZING?!!?!??!
Usage Note: When new words come into the language, they often have different forms for a period until one form wins out over the others. There are occasions when competing forms remain in use for a long time. The word disk and its descendant compound compact disk represent good examples of this phenomenon. Disk came into English in the mid-17th century and was originally spelled with a k on the model of older words such as whisk. The c-spelling arose a half century later as a learned spelling derived from the word's Latin source discus. Both disc and disk were used interchangeably into the 20th century, with people in Britain tending to use disc more often, and Americans preferring disk. The spellings also began to be sorted out by function. Late in the 19th century, for reasons that are not clear, people used disc to refer to the new method of making phonograph recordings on a flat plate (as opposed to Edison's cylindrical drum). In any case, the c-spelling became conventional for this sense, which is why we listen to disc jockeys and not disk jockeys. In the 1940s, however, when American computer scientists needed a term to refer to their flat storage devices, they chose the spelling disk, and this became conventionalized in such compounds as hard disk and floppy disk. When the new storage technology of the compact disk arose in the 1970s, both c- and k-spellings competed for an initial period. Computer specialists preferred the familiar k-spelling, while people in the music industry, who saw the shiny circular plates as another form of phonograph record, referred to them as compact discs. These tendencies soon became established practice in the different industries. This is why we buy compact disks in computer stores but get the same storage devices with different data as compact discs in music stores. Similarly, the computer industry created the optical disk, the format that the entertainment industry used to create the videodisc.