MBC4 (Game Boy mapper)

MBC4 is a Game Boy mapper (likely in a chip) by Nintendo, and other unknown parties (though possibly Marigul Management brought about its inception) with memory bank controller support. No licensed games actually use it, and it is not known what it looks like.

It would have possibly been used for games/cartridges with the 64GB Cable to enable interactions (including asymmetric ones) between a Nintendo 64 and Game Boy (a technology later revisited for the Nintendo GameCube Game Boy Advance Cable and then the Wii U GamePad); this was proposed during Marigul's game DT: Lords of Genomes, but in the end the functionality between the Nintendo 64 was scrapped and Nintendo did not publish it.

Another theory is that DT: Lords of Genomes was not the only software to use the 64GB Cable and MBC4 chip; code in the Nintendo 64DD games Mario Artist: Paint Studio and Mario Artist: Communication Kit suggests MBC4 may have been involved with Game Boy Printer Color using the GB Printer Cartridge (GBプリンタカートリッジ).

A source code leak for the Nintendo 3DS has some emulation support for MBC4 in a Game Boy/Color, Game Boy Advance, Nintendo Entertainment System or Famicom Disk System), but research is incomplete at this time; like certain other official mappers like MBC6, research is in its infancy.

MBC4 is similar to MBC3 but without the Real-Time Clock feature and has cancelled support for a Nintendo 64 controller/using the cable involving RAM bank 0x40.