SirPrimalform: I believe nowadays, disc means a flat circular object (this includes CDs, DVDs, LPs, etc.), wheras disk is short for diskette.
jamyskis: No it isn't. The word diskette is an American invention to describe the fact that the 3.5" discs that were coming in at the time were smaller. The spelling just got carried over, and UK versions of Windows are still in US English (thereby also spelling disc as disk), but the correct UK spelling of disc is still disc.
First, read my edit above. ;)
Second, read bazilisek's link.
Third, in the UK disk
is used, but only as a shortening of diskette (and in American software where they like to call most things disks).
jamyskis: Edit: Just noticed your edit. Disc isn't the diminutive form, diskette is.
I never said disc was the diminutive form, re-read my post. :P