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RetroBIOS

Kega Fusion

Kega Fusion emulates Sega Mega Drive, Sega Mega CD, Sega 32X and 4 more systems. It picks the BIOS for your game's region: us_scd1_9210.bin (North America and Latin America), jp_mcd1_9111.bin (Japan) or eu_mcd1_9210.bin (Europe and Oceania). 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 standalone
Classification Other
Source https://www.carpeludum.com/kega-fusion/
Upstream closed-source
Version 3.64
Profiled 2026-10-20
Profile YAML, JSON
Cores kega-fusion
Systems Sega Mega Drive, Sega Mega CD, Sega 32X, Sega Master System, Sega Game Gear, Sega SG-1000, Sega SF-7000
Author Steve Snake
Install this emulator's files

With RetroBat: the installer finds RetroBat and its BIOS folder, then downloads only the files Kega Fusion 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 kega-fusion
Technical notes

Sega 8 and 16-bit emulator by Steve Snake, distributed as a closed Windows binary. The build read is Fusion.exe 3.64 (NOMAPLE), dated 6 March 2010, sha1 4842ddbfbdfeb909b134f28ce25f02ab59b38453, the copy RetroBat installs as kega-fusion (version 0.10.03.06). The executable is not packed, offsets below are virtual addresses in it.

Every system ROM is a path stored in Fusion.ini, kept in a settings table of key name, buffer and type (0x5b16a8-0x5b1d10): SMSUSABIOS, SMSJAPBIOS, SMSEURBIOS, GGBIOS, SF7000IPL, GenesisBIOS, SCDUSABIOS, SCDJAPBIOS, SCDEURBIOS, 32XM68KBIOS, 32XMSH2BIOS and 32XSSH2BIOS. Before the ini is read the 8-bit, SF-7000 and Genesis paths are cleared (0x44b3ed-0x44b40b) and the Mega CD and 32X ones get defaults: C:\SegaCDBIOS\us_scd1_9210.bin, jp_mcd1_9111.bin and eu_mcd1_9210.bin, and c:\32XBios\32X_G_BIOS.bin, 32X_M_BIOS.bin and 32X_S_BIOS.bin (0x44b662-0x44b74d). Those are the only file names the binary fixes. Each file is opened with fopen "rb" and read with a fixed count, no length, checksum or header is compared.

CDTray.raw, Cursor_8.raw, STATIC_8.RAW and gg_nor.all are looked up by name in an archive embedded in the executable (0x47a530), not on disk. Plugins (*.rpi) and the KGV1 video codec ship with the program. Fusion.ini, battery saves (.srm, .brm, .crm) and states are written by the program.

Files

Section titled “Files”

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

File Region Required
us_scd1_9210.bin North America and Latin America for Sega Mega CD
jp_mcd1_9111.bin Japan for Sega Mega CD
eu_mcd1_9210.bin Europe and Oceania for Sega Mega CD
32X_G_BIOS.bin - no
32X_M_BIOS.bin - no
32X_S_BIOS.bin - no
bios_MD.bin - no
bios_U.sms - no
bios_J.sms Japan no
bios_E.sms - no
bios.gg - no
SF7000.ROM - no

In this collection: 12 in repo and 0 missing.

Required

Section titled “Required”

us_scd1_9210.bin required for Sega Mega CD in repo Region: North America and Latin America

Sega CD (USA) boot ROM

  • Opened from SCDUSABIOS when a disc starts in the USA region and read as 128 KB. A failed open shows "Please configure USA BIOS in OPTIONS->SET CONFIG->SEGA CD" under the title "BIOS Not Found" and writes 60 FE, a branch to itself, at the reset vector, so nothing boots.

jp_mcd1_9111.bin required for Sega Mega CD in repo Region: Japan

Mega CD (Japan) boot ROM

  • Opened from SCDJAPBIOS for the Japanese region, same 128 KB read and same lock when it is missing, with the JAP message.

eu_mcd1_9210.bin required for Sega Mega CD in repo Region: Europe and Oceania

Mega CD (Europe) boot ROM

  • Opened from SCDEURBIOS for the European region, same 128 KB read and same lock when it is missing, with the EUR message. With country autodetect on (the default), the disc's security byte at 0x20B picks the region: 0x7A USA, 0xA1 JAP, 0x64 EUR. EUR is the only branch that sets the PAL version bits (0xC0) and 50 Hz, so Australian discs take it too.

Optional

Section titled “Optional”
9 files

32X_G_BIOS.bin optional in repo HLE fallback

32X 68000 BIOS

  • Source: offset 0x44b718-0x44b724 in Fusion.exe, offset 0x4c81ae-0x4c81ed in Fusion.exe, offset 0x4c8287-0x4c833c in Fusion.exe
  • Collection copy: bios/Sega/32X/32X_G_BIOS.BIN
  • Platforms: BizHawk: 32X_G_BIOS.BIN, RetroBat: 32X_G_BIOS.BIN, RetroDECK: bios/32X_G_BIOS.BIN
  • First 256 bytes read from 32XM68KBIOS. When any of the three 32X files fails to open, the loaded images are discarded and replacement code held in the executable is copied over all three areas.

32X_M_BIOS.bin optional in repo HLE fallback

32X master SH-2 BIOS

  • Source: offset 0x44b730-0x44b73c in Fusion.exe, offset 0x4c81f1-0x4c8238 in Fusion.exe, offset 0x4c8287-0x4c833c in Fusion.exe
  • Collection copy: bios/Sega/32X/32X_M_BIOS.BIN
  • Platforms: BizHawk: 32X_M_BIOS.BIN, RetroBat: 32X_M_BIOS.BIN, RetroDECK: bios/32X_M_BIOS.BIN
  • 2 KB read from 32XMSH2BIOS. Same all-or-nothing replacement as the 68000 BIOS.

32X_S_BIOS.bin optional in repo HLE fallback

32X slave SH-2 BIOS

  • Source: offset 0x44b743-0x44b74d in Fusion.exe, offset 0x4c823c-0x4c8283 in Fusion.exe, offset 0x4c8287-0x4c833c in Fusion.exe
  • Collection copy: bios/Sega/32X/32X_S_BIOS.BIN
  • Platforms: BizHawk: 32X_S_BIOS.BIN, RetroBat: 32X_S_BIOS.BIN, RetroDECK: bios/32X_S_BIOS.BIN
  • 1 KB read from 32XSSH2BIOS. Same all-or-nothing replacement as the 68000 BIOS.

bios_MD.bin optional in repo

Mega Drive TMSS boot ROM

  • Read as 2 KB from GenesisBIOS when that path is set, and skipped when the open fails. The code fixes no file name, the user picks it in the Genesis settings.

bios_U.sms optional in repo

Master System (USA) boot ROM

  • Read from SMSUSABIOS, up to 512 KB, for the USA region unless SMSBIOSDisable is set. A missing file leaves the cartridge to start directly. No file name is fixed by the code. The header nibble at 0x7FFF tells Japan from export only: an export cart gets USA or EUR from the CountryOrder setting (USA by default), or from a CRC32 list held in the executable.

bios_J.sms optional in repo Region: Japan

Master System (Japan) boot ROM

  • Read from SMSJAPBIOS for the Japanese region, same rules as the USA image.

bios_E.sms optional in repo

Master System (Europe) boot ROM

  • Read from SMSEURBIOS for the European region, same rules as the USA image. EUR comes from the CountryOrder setting or the CRC32 list, never from the header.

bios.gg optional in repo

Game Gear boot ROM

  • Read from GGBIOS, up to 512 KB, in Game Gear mode unless SMSBIOSDisable is set, and skipped when the open fails. No file name is fixed by the code.

SF7000.ROM optional in repo

Sega SF-7000 IPL

  • Read as 8 KB from SF7000IPL when the SF-7000 is emulated and mirrored to fill 16 KB. A missing file is skipped without a message. No file name is fixed by the code.

Next steps

Section titled “Next steps”
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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.