NEC PC Engine collectors can feel confused by the various system cards and game types.
NEC released cards to boost the systems’ memory capacity. Each card corresponds to a set of NEC consoles.
Arcade Card: Nec Pc-Engine Arcade Card Duo Rom Ram HuCARD
Like the Arcade Card Pro, the Nec PC Engine Arcade Card Duo preforms the function of allowing NEC systems to play Arcade CD-ROM² games.
Where they differ is that the Duo version is meant for Duo systems, while the Pro version is meant for the older NEC consoles.
A few more things should be kept in mind about system cards and game formats.
Similar to HuCards, a system card can only be used in the region it was meant for.
The cards sold on RETROPIXL are only valid with Japanese versions of the consoles.
In terms of games, it is possible to tell what format a game is simply by looking at the front of its manual or box.