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 Duo, the Nec PC Engine Arcade Card Pro 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.