Unless I'm mistaken, the disk/disc difference is mostly whether the tye of data storage is magnetic or optical (as long as the physical form is a disc), though I believe magneto-optical media used "disk" as the storage itself was magnetic and the optics merely heated the bits that should be written by the magnet. As for the origin of the words, your guess is as good as mine or better.

This is my definition also. The same can be said for hard drives.

For reference, I am Australian, and this is what I believe to be common convention here.

Sounds about right... 3.5" disk, compact disc...

Dragons Lair came on 13 5¼" Floppy Disks apparently.

Do we only count games or does the fact Windows 95 came on 20 3½ Floppy Disks count.
I think there is a version of 98 on Floppy Disk as well not sure how many Floppy Disks though but I expect it is a lot.