[sandworm101]

Also, disk is also used in "diskette", whereas disc stands alone. So as magnetic disks shrank and were called disketts on and off, they kept that spelling. Optical discs never really shrank over the years, never being called discettes.

[oneplane]

When they shrank the disc it just became minidisc ;-) But that was technically MO, not just optical. And: it was in a cartridge so I suppose they really should have called it minidisk.