Its most defining, and troublesome, feature was its internal ROM. This protected, internal memory contained vital code that the chip needed to function, acting as a form of copy protection. While the external music data was stored on separate, readable chips, the internal "brains" of the sound system were locked away, preventing anyone from understanding exactly how it worked. This left MAME developers with no choice but to rely on imperfect simulation for the NMK004 sound, resulting in emulated games where the audio was often incorrect, choppy, or missing entirely.
Genuine BIOS updates carry an encrypted signature from the vendor to pass Secure Boot checks.
: Some users access "Advanced" or "Secret" BIOS menus for undervolting or performance tuning, but this should only be done using the device's original firmware.
