When you download a ROM set for a game like Thunder Dragon 2 , the archive is not a single file. It is a zip container holding multiple .bin files (often labeled nmk001.bin , nmk002.bin , nmk003.bin , nmk004.bin , etc.). Each file corresponds to a specific physical EPROM chip on the original arcade printed circuit board (PCB).
For decades, emulators like MAME struggled with NMK titles because the internal logic of this chip was a "black box". In 2014, a developer known as successfully cracked the protection.
The "nmk004.bin" file is a legendary component in the arcade emulation community, representing the successful conclusion of a 20-year-long effort to reverse-engineer and dump a highly secure sound chip. What is NMK004?