Important notes when choosing your Sega CD Bios:

1.) Please use a bios that matches your models Sega CD as Model 1 bioses will not work in Model 2 consoles and vice-versa due to the disc loading style between these consoles.

2.) There are currently some Japanese Mega CD game compatibility issues with all USA and European bioses. For 100% compatibility, it is recommended to use a Japanese bios or do a dual bios mod. Japanese Mega CD bioses are compatible with USA consoles, but Japanese Mega CD bioses will not work in European consoles with the exception of one bios. For a list of games that have compatibility issues, please see below:

Games that work with USA (NTSC-U) and European (PAL) bioses that have a very minor graphical issue:
Gambler Jikocyushinha 2 (First copyright screen has slight corruption, but over all works 100%)

Games that work with USA (NTSC-U) and European (PAL) bioses while pressing C and Start after disc loading is completed:
Aisle Lord
Fhey Area

Games that are currently not working with USA (NTSC-U) and European (PAL) bioses:
Heavy Nova
Ishii Hisaichi no Daisekai
Sengoku Densyo

USA:
Sega CD Model 1 [NTSC-U] [Ver. 1.10]
Sega CD Model 2 [NTSC-U] [Ver. 2.00]
Sega CDX [NTSC-U] [Ver. 2.21] (Will need to do some reworking/heavy wiring because the package type of the bios of this console is SMD)
JVC E'Eye [NTSC-U] [Ver. 2.00] (Will need to do some reworking/heavy wiring because the package type of the bios of this console is SMD)

Japan:
Mega CD Model 1 [NTSC-J] [Ver. 1.00]
Mega CD Model 1 [NTSC-J] [Ver. 1.00] [PAL Compatible - For use with model 1's only]
Mega CD Model 2 [NTSC-J] [Ver. 2.00]
Wondermega [NTSC-J] [Ver. 1.00] (Will need to do some reworking/heavy wiring because the package type of the bios of this console is SMD)
Wondermega M2 [NTSC-J [Ver. 2.00] (Will need to do some reworking/heavy wiring because the package type of the bios of this console is SMD)

European:
Mega CD Model 1 [PAL] [Ver. 1.00]
Mega CD Model 2 [PAL] [Ver. 2.00]
Multi Mega CD [PAL] [Ver. 2.21] (Will need to do some reworking/heavy wiring because the package type of the bios of this console is SMD)