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RetroBIOS

Genesis Plus GX

Genesis Plus GX emulates Sega Mega Drive, Sega Mega CD, Sega Master System and 3 more systems. It picks the BIOS for your game's region: bios_CD_U.bin (North America and Latin America), bios_CD_E.bin (Europe and Oceania) or bios_CD_J.bin (Japan). The 9 other files are optional. A required file is needed only by the machines that use it. Each file below cites the line of source code that reads it.

About this profile
Detail Value
Type libretro
Classification Community fork
Source https://github.com/libretro/Genesis-Plus-GX
Upstream https://github.com/ekeeke/Genesis-Plus-GX
Version v1.7.4, stated in libretro/libretro.c
Revision libretro/Genesis-Plus-GX@60bee4c72485, ekeeke/Genesis-Plus-GX@c7ecd07f0a08
Profiled 2026-03-23
Profile YAML, JSON
Cores genesis_plus_gx, genesisplusgx, genplus, genesisplusgx_ex, genesis_plus_gx_cart_special, genesis-plus-gx
Systems Sega Mega Drive, Sega Mega CD, Sega Master System, Sega Game Gear, Sega SG-1000, Sega Pico
Install this emulator's files

The installer finds your setup and its BIOS folder, then downloads only the files this emulator reads there and checks each one.

Open the Start menu. Type PowerShell and open it. Paste the line. Press Enter.

PowerShell
&([scriptblock]::Create((irm https://abdess.github.io/retrobios/i.ps1))) --emulator genesis_plus_gx
Platform details

  • megacd:

    • bootrom_size: 131072
    • source_ref: core/cd_hw/scd.h:73 (emulator code, libretro port)
    • note: CD boot ROM region is auto-detected from disc image header. Hardware model detected from boot ROM string at offset 0x120: WONDER-MEGA BOOT -> Wondermega WONDERMEGA2 BOOT -> Wondermega M2 / X'Eye CDX BOOT ROM -> CDX / Multi-Mega

  • megadrive:

    • tmss_rom_size: 2048
    • source_ref: libretro/libretro.c:3648-3666 (libretro glue)
    • note: TMSS boot ROM validated by checking "GENESIS OS" at offset 0x120. Only loaded when genesis_plus_gx_bios core option is enabled.

  • mastersystem:

    • bios_max_size: 4194304
    • source_ref: core/loadrom.c:504-527 (emulator code, libretro port)
    • note: BIOS ROM loaded into cart.rom + 0x400000. SEGA mapper assumed for ROMs larger than 48KB, otherwise no mapper. Region selected based on current region_code setting.

  • gamegear:

    • bios_max_size: 4194304
    • source_ref: core/loadrom.c:467-489 (emulator code, libretro port)
    • note: Handles 1KB Majesco GG BIOS (mapped to $0000-$03FF) and standard larger BIOS ROMs.
Technical notes

Genesis Plus GX is a Sega 8/16-bit emulator covering SG-1000, Master System, Game Gear, Mega Drive/Genesis, and Mega CD/Sega CD.

BIOS loading is handled by load_bios() in core/loadrom.c. The libretro port resolves filenames from the system directory in libretro/libretro.c:3516-3527.

Mega CD BIOS is required to boot CD images (load fails without it). Master System, Game Gear, and Mega Drive BIOS files are optional boot ROMs gated behind the "genesis_plus_gx_bios" core option (config.bios). Lock-on ROMs (Game Genie, Action Replay, Sonic & Knuckles) are optional and loaded only when the corresponding lock-on feature is enabled.

Files

Section titled “Files”

12 files. One of 3 is required, for your games' region. 9 are optional.

In this collection: 12 in repo and 0 missing.

Required

Section titled “Required”
FileStatus

bios_CD_U.bin

  • System: Sega Mega CD
  • Sega CD (NTSC-U) boot ROM. Loaded for REGION_USA, which get_region sets for every disc whose security byte is neither 0x64 (Europe) nor 0xa1 (Japan) (core/loadrom.c:1065-1078).
Source
  • Asked for by: emulator code, libretro port
  • Source: core/loadrom.c:409 (emulator code, libretro port)
required for Sega Mega CD in repo Region: North America and Latin America

bios_CD_E.bin

  • System: Sega Mega CD
  • Mega CD (PAL) boot ROM. Loaded for REGION_EUROPE, set by security byte 0x64 at 0x20b, the only PAL branch for Australian discs (core/loadrom.c:1065-1069).
Source
  • Asked for by: emulator code, libretro port
  • Source: core/loadrom.c:412 (emulator code, libretro port)
required for Sega Mega CD in repo Region: Europe and Oceania

bios_CD_J.bin

  • System: Sega Mega CD
  • Mega CD (NTSC-J) boot ROM. Loaded for default/Japan region.
Source
  • Asked for by: emulator code, libretro port
  • Source: core/loadrom.c:415 (emulator code, libretro port)
required for Sega Mega CD in repo Region: Japan

Optional

Section titled “Optional”
FileStatus

bios_U.sms

  • System: Sega Master System
  • Master System (NTSC-U) boot ROM. Snail maze game built in. REGION_USA is the default of sms_cart_region_detect for any export header outside the PAL CRC list, so European, Australian and Brazilian cartridges outside that list load it too (core/cart_hw/sms_cart.c:831-874).
Source
  • Asked for by: emulator code, libretro port
  • Source: core/loadrom.c:511 (emulator code, libretro port)
in repo Region: North America, Latin America, Europe and Oceania

bios_E.sms

  • System: Sega Master System
  • Master System (PAL) boot ROM. Snail maze / Sonic built in. REGION_EUROPE comes only from CRC lists of Codemasters and PAL-timing games, Brazilian ones included, or the PAL option (core/cart_hw/sms_cart.c:167-171, 245-264, core/loadrom.c:1161-1164).
Source
  • Asked for by: emulator code, libretro port
  • Source: core/loadrom.c:514 (emulator code, libretro port)
in repo

bios_J.sms

Source
  • Asked for by: emulator code, libretro port
  • Source: core/loadrom.c:517 (emulator code, libretro port)
in repo Region: Japan

bios.gg

  • System: Sega Game Gear
  • Game Gear boot ROM (Majesco 1KB or standard). Shows startup logo.
Source
  • Asked for by: emulator code, libretro port
  • Source: core/loadrom.c:480 (emulator code, libretro port)
in repo

bios_MD.bin

  • System: Sega Mega Drive
  • Mega Drive TMSS boot ROM. Shows 'Produced by or under license' screen.
Source
in repo

ggenie.bin

  • System: Sega Mega Drive
  • Game Genie ROM. Loaded when Game Genie lock-on is enabled.
Source
in repo

areplay.bin

  • System: Sega Mega Drive
  • Action Replay (Pro) ROM. Loaded when Action Replay lock-on is enabled.
Source
in repo

sk.bin

  • System: Sega Mega Drive
  • Sonic & Knuckles ROM. Required for S&K lock-on feature.
Validation and source
in repo

sk2chip.bin

  • System: Sega Mega Drive
  • Sonic & Knuckles UPMEM ROM. Used by Sonic 2 & Knuckles lock-on.
Validation and source
in repo

Next steps

Section titled “Next steps”
.

Maintained by Abdess on GitHub. Report a problem.

Packs from release v2026.10.10, .

MIT for the tooling and metadata. BIOS and firmware files are third-party system software, preserved for personal backup, archival and interoperability.