Skip to content
RetroBIOS

Genesis Plus GX Expanded

Genesis Plus GX Expanded 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 Enhanced fork
Source https://github.com/BillyTimeGames/Genesis-Plus-GX-Expanded-Rom-Size
Upstream https://github.com/ekeeke/Genesis-Plus-GX
Version v1.7.4
Revision BillyTimeGames/Genesis-Plus-GX-Expanded-Rom-Size@dea3528cc0e3, ekeeke/Genesis-Plus-GX@e366ca817f5b
Built by batocera, retrobat, under its core name. The libretro buildbot does not publish this build.
Profiled 2026-10-23
Profile YAML, JSON
Cores genesis_plus_gx_expanded, genesisplusgx-expanded
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://raw.githubusercontent.com/Abdess/retrobios/main/install.ps1))) --emulator genesis_plus_gx_expanded
Technical notes

Fork of Genesis Plus GX branched from ekeeke's tree at e366ca8 (May 2022). Makefile.libretro builds it with MAXROMSIZE 93554432 for Sega Channel dumps and large hacks, and it adds a Paprium mapper (core/cart_hw/paprium.h). RapidEdwin08/Genesis-Plus-GX-Expanded-Rom-Size, which Batocera 43.1 builds as genesisplusgx-expanded at a0b5a033 (Batocera package/batocera/emulators/retroarch/libretro/libretro-genesisplusgx-expanded/libretro-genesisplusgx-expanded.mk:7), carries the same core/, libretro/ and Makefile.libretro as this pin, and so does its tip 181e8f93. RetroBat ships genesis_plus_gx_expanded_libretro.dll from its own core repository, and its strings carry the same file names and the Paprium track list.

The system files are those of the mainline core, under the same names and read the same way: fill_pathname_join builds all twelve paths from the system directory (libretro/libretro.c:3581-3592). The Mega CD boot ROM of the disc's region is required, the Master System, Game Gear and Mega Drive boot ROMs are read only with the genesis_plus_gx_bios option, and the lock-on ROMs only with the matching lock-on cartridge.

The Paprium mapper streams its music from a paprium folder next to the game, MP3 tracks named after the soundtrack (core/cart_hw/paprium.h:158-261). Those belong to the game release. The paprium.wav reader sits under if(0) (core/cart_hw/paprium.h:2748-2760) and never runs.

Files

Section titled “Files”

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

File Region Required
bios_CD_U.bin North America and Latin America for Sega Mega CD
bios_CD_E.bin Europe and Oceania for Sega Mega CD
bios_CD_J.bin Japan for Sega Mega CD
bios_U.sms North America, Latin America, Europe and 1 more no
bios_E.sms - no
bios_J.sms Japan no
bios.gg - no
bios_MD.bin - no
ggenie.bin - no
areplay.bin - no
sk.bin - no
sk2chip.bin - no

In this collection: 12 in repo and 0 missing.

Required

Section titled “Required”

bios_CD_U.bin required for Sega Mega CD in repo Region: North America and Latin America

  • Sega CD (NTSC-U) boot ROM. Loaded for REGION_USA, which get_region sets for every disc whose security byte at 0x20b is neither 0x64 nor 0xa1 (core/loadrom.c:1056-1070).

bios_CD_E.bin required for Sega Mega CD in repo Region: Europe and Oceania

  • Mega CD (PAL) boot ROM. Loaded for REGION_EUROPE, set by security byte 0x64 (core/loadrom.c:1059-1061).

bios_CD_J.bin required for Sega Mega CD in repo Region: Japan

  • Mega CD (NTSC-J) boot ROM. Loaded for every other region code.

Optional

Section titled “Optional”
9 files

bios_U.sms optional in repo Region: North America, Latin America, Europe and Oceania

  • Master System (NTSC-U) boot ROM, loaded for REGION_USA when the bios option is on. REGION_USA is the default of sms_cart_region_detect for any export header outside its CRC list, so European, Australian and Brazilian cartridges outside that list load it too (core/cart_hw/sms_cart.c:865-866).

bios_E.sms optional in repo

  • Master System (PAL) boot ROM, loaded for REGION_EUROPE when the bios option is on.

bios_J.sms optional in repo Region: Japan

  • Master System (NTSC-J) boot ROM, loaded for the Japanese region codes when the bios option is on.

bios.gg optional in repo

  • Game Gear boot ROM, 1 KB Majesco image or a larger one, loaded when the bios option is on.

bios_MD.bin optional in repo

  • Mega Drive TMSS boot ROM. 2 KB read, accepted when "GENESIS OS" sits at 0x120.

ggenie.bin optional in repo

  • Game Genie ROM, read when the Game Genie lock-on is selected.

areplay.bin optional in repo

  • Action Replay (Pro) ROM, read when the Action Replay lock-on is selected.

sk.bin optional in repo

  • Sonic & Knuckles ROM for the lock-on cartridge, kept only when the read fills 2 MB.

sk2chip.bin optional in repo

  • Sonic & Knuckles UPMEM ROM, read after sk.bin and kept only when the read fills 256 KB.

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.