Sega Mega-CD 32X
From Sega Retro
The Sega Mega Drive console received two add-on hardware upgrades during its life time: the Sega Mega CD and Sega 32X. It was possible to install both of these on the same base console, creating a system called the Sega Mega CD 32X (Japan and PAL regions) or Sega CD 32X (USA). This opened the possibility of software that could utilise both the Mega CD's enhanced storage capacity and ability to play Red Book CD audio, and the 32X's enhancements in graphics and sound capabilities.
Five games were released that require both add-on units in order to be played. All of these titles are full motion video based games, that were previously available as standalone Mega CD games, which later had their FMV assets upgraded to take advantage of the 32X's improved graphics. As such, all Sega Mega CD 32X titles are on CDs, the cart slot of the 32X being unused.