Spelling of disc

"Disc" and "disk" are both variants of the English word for objects of a generally thin and cylindrical geometry. The differences in spelling correspond both with regional differences and with different senses of the word. For example, in the case of flat, rotational data storage media the convention is that the spelling "disk" is used for magnetic storage (e.g. hard disks) while "disc" is used for optical storage (e.g. compact discs, better known as CDs). When there is no clear convention, the spelling "disk" is more popular in American English, while the spelling "disc" is more popular in British English.
Disk.
The earlier word is "disk", which came into the English language in the middle of the 17th century. In the 19th century, "disk" became the conventional spelling for audio recordings made on a flat plate, such as the gramophone record. 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).
UK vs. US.
By the 20th century, the "k" spelling was more popular in the United States, while the "c" variant was preferred in the UK. In the 1950s, when the American company IBM pioneered the first hard disk drive storage devices, it used the "k" spelling. Consequently, in computer terminology today it is common for the "k" word to refer mainly to magnetic storage devices (particularly in British English, where the term "disk" is sometimes regarded as a contraction of "diskette", a much later word and actually a diminutive of "disk").
Computer discs.
Some latter-day competitors to IBM prefer the "c"-spelling. 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.
Medical editing.
The words "disc" and "disk" can appear frequently in medical journals and textbooks, especially those in ophthalmology and orthopedics, and thus style guides often foster consistency by giving rules for which contexts take which spelling. AMA style for this topic is used by many publications. AMA says, "For ophthalmologic terms, use "disc" (eg, "optic disc"); for other anatomical terms, use "disk" (eg, "lumbar disk"). In discussions related to computers, use "disk" (eg, "floppy disk, disk drive, diskette") (exceptions: "compact disc, videodisc")."
Sports.
Disc sports, or disc games, are a category of activities which involve throwing and/or catching a flying disc. Participants of disc sports consistently use the "c" spelling when describing the sports equipment used in these activities, which includes team sports such as ultimate or individual sports such as disc golf.