These cartridges (there are several, almost every CD-I model uses
a different one) gives the possibility to play movies, concerts, etc.
on Video CDs.
It was also used to enable full-screen full motion video on different games (for example Dragon's Lair and Space Ace) and to add video footage to many interactive titles (like dictionaries, reference programs, etc.).
(I am sorry but I have only this picture... and
it's only a particular of the DVC... I hope to find a better pic
Note that not every CD-I model has an expansion port that could accept a Digital Video Cartridge. In particular early models did not have this option since VideoCD support was only an optional feature and not part of the "Green Book".
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