Minidiscs were used for data almost exclusively in Japan, they are small rewritable CDs in a plastic shell.
(I am the only person I know to have owned a Minidisc player.)
Legend of the Galactic Heroes was a WORM disk: https://images-na.ssl-images-amazon.com/images/I/41eTWeeR8XL...
I also owned a couple minidisk players, a real underrated format.
In somewhat later material, DVD-RAM also shows up in caddies.
Minidiscs were used for data almost exclusively in Japan, they are small rewritable CDs in a plastic shell.
(I am the only person I know to have owned a Minidisc player.)