Nintendo opens up one of its secret storage rooms

[numberwang]

If you didn't knew, the Japanese Famicon supported add-in chips in the cartridge, the EUSA NES did not. One example is the enhanced music in Akumajou Densetsu (Famicom) vs. Castlevania III (NES).

https://www.youtube.com/watch?v=Rh-vkpjyMTw