Prologue:  The dictionaries of the English-speaking countries do
not _dictate_ word meanings; rather, they _reflect_ common usage,
and the spoken language is free to evolve dynamically.  In
some countries, notably France, the Guardians_of_Words wage a
humorous, futile battle in attempting to dictate "proper"
vocabulary!

Wayne Stahnke asked "Do music boxes use 'discs' or 'disks', and
why?"

Robin Cherry at BBC noted, "I have understood the situation to be
that disks can be written upon whereas discs cannot. Therefore
musical box discs would be discs, but computer disks would be
disks."

Reasoning that -- since we in this group deal with antiquities -- we
should research the jargon in the same era as our hobby, I checked
the 1930 edition of the giant Webster's New International Dictionary
(7 kg), which says:

   disc = disk

Following that abrupt dismissal I found

   disk  n. also disc. [L. discus, G. diskos]
     1. A discus; a quoit.
     2. A flat circular plate; as, a _disk_ of metal or paper.

Therefore American _usage_ up to 1930 was "disk".  I don't have an
Oxford dictionary, but the "English side" of my German-to-English
translating dictionary (1990) was edited by the scholars at Oxford
University Press.  Surprise:

   disk - see disc
   (disc - no entry!)

The German term for the musical box disk/disc is "die Platte" - a
plate, or sheet; also a [phonograph] record.  I wager that "Platte", as
a musical "record" in German, was used first with the music box, and
then extended to phonograph records.  And I also wager that the same
thing happened in English: the music box "disk" turned into the
phonograph "disk".  I think the spelling "disc" became popular in
America with the invention of the "magnetic disc memory", and this
spelling may now be predominant.

I don't know for sure which spelling was used in the old advertisements
for musical boxes, but that's the spelling I'd prefer to use.

(By the way, what does the modern Oxford dictionary say about usage
in Great Britain?)

-- Robbie Rhodes