Thunder Force IV was the very first game with a sophisticated regional lockout chip, meaning that unlike previous Mega Drive games you could not play the Japanese version on a European Mega Drive or Sega Genesis (and vice versa) with a simple pass through adapter.
Thunder Force IV was the very first game with a sophisticated regional lockout chip. You could not play the Japanese version on a European Mega Drive or Sega Genesis (and vice versa) with a simple pass through adapter. This is unlike previous Mega Drive games. This was what Thunder Force IV was meaning.