Let me clear this up even more since there is some bad information being passed here you do not need the bios set with split merged or non-merged. I don't ever download the bios set I can play any game that requires a bios same with devices all of those files are included in your set if you have a bios set then they are duplicated in your MAME full set check and compare I guarantee you will see I'm correct in this. The bios set that comes from PD also contains the devices look at the name of the set it is called bios-devices.