disk/c

http://d.hatena.ne.jp/kanose/20041118#diskdisc2

http://dictionary.reference.com/search?q=compact%20disk

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.

訳ではなくて感想交えて大意。

もともとは１７世紀半ばに英語にこの言葉がラテン語discusから入ってきたときは英語の発音の似たwhiskみたいな単語と同じ方式でdisk。で半世紀すぎて、もとのラテン語にひかれてdiscのつづりをするひとも現れた。この時点では趣味というか癖みたいなもの。ただしどっちかというとイギリス人はdiscとつづり、アメリカ人はdiskを好んだ。これはもともとcとつづるのは衒学的な感じがするというのと通じていそう。

で、十九世紀末にレコードが発明される。で、レコードの意味のときはdiscのcつづりが区別のため使われるようになる。disc jockey つぎに1940年代、コンピュータ屋さんが円盤状の記録媒体を呼ぶ名前を必要としたとき、diskのつづりを選んだ。hard disk。この時点まではまぎれがない。

問題は、CDという両方で使われる媒体が1970年代はじめに発明されたこと。で、しばらくは両方のつづりが個々人で競合したけれども、やっぱりコンピュータ業界と音楽業界でdiskとdiscを使う傾向が分かれた。ついで、このおおまかな呼び方の傾向の違いははっきりと慣行として定着。なので、光ディスクはdisk、ビデオディスクはdisc。

ということらしいです。実際にこの使い分けが厳密に今も行われているのかどうかはわからないですが。コンピュータ屋さんがdiskを選んだのはその当時は円盤状とはいえレコードとは特に似ていなかったからじゃないかと思いますがこれもよくわかりません。