R4 cartridge

It allows ROMs and homebrew to be booted on the Nintendo DS handheld system from a microSD card.

Since the 3DS's secure boot signature validation has been broken, this provides a useful means of installing custom firmware on a 3DS.

These flashcards, referred to as clones, commonly add words to their names to denote their features such as SDHC if it supports SDHC microSD cards, RTS if it has Real Time Save support, and DSi or 3DS often paired with changing R4 to R4i if it works on the Nintendo DSi or 3DS consoles.

It is also very common for clone cartridges to include words such as Gold, Plus, Ultra, and Dual-Core which only serve to make the card sound impressive.

R4 flash cartridges are banned in some countries due to copyright infringement lawsuits from Nintendo.

After the news broke, Nintendo released on a statement saying that they do support game developers that create their own applications legitimately.

[11] In 2012, the Japanese Ministry of Economy, Trade, and Industry revealed that the importing of R4 cards, and similar devices, is now punishable by law.

The Tokyo district court ruled that the sellers of the R4 cards owed Nintendo and 49 other video game developers ¥95,625,000.

Curiously, in another trial held in 2016 Court of Catania declared flashcards legal since they have been exchanged for microSD-to-DScart adapters, citing the fact the R4 is not able to run any copyrighted code without a kernel, which is not sold with the flashcard, and the hardware-embedded protection breaking functionalities were considered legitimate to run unsigned code.