The word “Disk” refers to a magnetic devise/media that that can be written to via microscopic magnetized needles on the disk's surface. Examples to Disk are Computer Disk, “Floppy Disk”, and Hard Drive Disk.
Whereas the word “Disc” refers to a optical devise/media that can be written to and read using a low-powered laser beam., such as musical box “Disc”, Compact Disc, and Digital Versatile Disc.
According to
http://www.wsu.edu/~brians/errors/disc.h… ,
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“Compact disc” is spelled with a “C” because that’s how its inventors decided it should be rendered; but a computer hard disk is spelled with a “K” (unless it's a CD-ROM, of course). In modern technological contexts, “disks” usually reproduce data magnetically, while “discs" reproduce it “optically,” with lasers.
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The best discussion of “Disk vs. Disk” was found at the following URL:
http://dictionary.laborlawtalk.com/Disk
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The divergence in spelling is due in part to the way in which the words originated. Disk came into the English language in the mid-17th century, and was modelled on words such as whisk; disc arose some time later, and was based on the original Latin root discus. In the 19th century, disc became the conventional spelling for audio recordings made on a flat plate, such as the gramophone record; this usage gave rise to the modern term disc jockey. Early BBC technicians differentiated between disks (in-house transcription records) and discs (the colloquial term for commercial gramophone records, or what the BBC dubbed CGRs).
By the 20th century, the c-spelling was more popular in British English, while the k-spelling was preferred in American English. In the 1940s, when the American company IBM pioneered the first hard disk storage devices, the k-spelling was used. In 1979 the European company Philips, along with Sony, developed the compact disc medium; here, the c-spelling was chosen, possibly because of the predominating British spelling, or because the compact disc was seen as a successor to the analogue disc record.
Whatever their heritage, in computer jargon today it is common for the k-spelling to refer mainly to magnetic storage devices, while the c-spelling is customary for optical media such as the compact disc and similar technologies. Even in the computing field, however, the terms are used inconsistently; software documentation often uses the k-spelling exclusively.
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