Last updated: September 2026
Saturn emulation has three different BIOS filenames in circulation and every emulator wants a different one. Beetle Saturn wants two files with part numbers for names. Kronos wants one called saturn_bios.bin in its own subfolder. Yabause will take the same file or run without it. People copy one in, get a black screen in a different core, and assume the dump is bad.
The dump is almost never bad. This page sorts out which file each emulator reads, the hashes to check them against, the folder on PC, Steam Deck, Android and the handheld firmwares, and the homebrew that dumps the BIOS from a Saturn you own. It is the Saturn entry in my RetroArch BIOS reference.
The Three Files
All three are 524,288 bytes (512 KB). Any of them is a complete, real Saturn BIOS. The names are conventions the emulators settled on, not different kinds of file.
| File | Region and version | MD5 | Who uses this name |
|---|---|---|---|
sega_101.bin | Japan, v1.01 (941228) | 85ec9ca47d8f6807718151cbcca8b964 | Beetle Saturn, Mednafen |
mpr-17933.bin | North America and Europe, v1.01a (941115) | 3240872c70984b6cbfda1586cab68dbe | Beetle Saturn, Mednafen |
saturn_bios.bin | Japan, v1.00 | af5828fdff51384f99b3c4926be27762 | Kronos, Yabause, YabaSanshiro |
Two things trip people up. First, saturn_bios.bin is not sega_101.bin renamed. It is the earlier v1.00 Japanese image with its own hash, and the cores that use that name treat the listed hash as a hint, not a requirement, so any valid Saturn BIOS renamed to saturn_bios.bin boots them. Second, Beetle Saturn has no region-free option: it loads the Japanese file for Japanese discs and the mpr-17933.bin file for everything else, and if you play both regions you need both files.
Optional extras
| File | What it is |
|---|---|
mpr-18811-mx.ic1 | The King of Fighters ‘95 cartridge ROM, MD5 255113ba943c92a54facd25a10fd780c |
mpr-19367-mx.ic1 | Ultraman: Hikari no Kyojin Densetsu cartridge ROM, MD5 1cd19988d1d72a3e7caa0b73234c96b4 |
stvbios.zip | The ST-V arcade board BIOS set, only for Kronos in ST-V mode |
The two cartridge ROMs are only for those two games, which shipped with a ROM cart the disc requires. Everything else runs from the disc image alone.
Which Emulator Wants Which File
| Emulator | BIOS | Behaviour without it |
|---|---|---|
| Beetle Saturn (RetroArch) | Required. sega_101.bin and mpr-17933.bin | Will not boot. No HLE. |
| Kronos (RetroArch) | Required. saturn_bios.bin | Will not boot. Kronos does not fall back to its HLE BIOS on its own. |
| Yabause (RetroArch) | Optional. saturn_bios.bin | Runs on an emulated BIOS with lower compatibility; multi-disc .m3u sets need the real file. |
| YabaSanshiro (RetroArch and Android) | Optional. saturn_bios.bin | Same as Yabause. |
| Mednafen standalone | Required. Both Beetle files | The ss.bios_jp and ss.bios_na_eu settings name them. |
My recommendation on PC and Steam Deck is Beetle Saturn, which is the Mednafen Saturn core and the most accurate of the lot. On Android handhelds it is too heavy, and YabaSanshiro is the one that runs at full speed; put the real BIOS in anyway, because the emulated one drops games.
Where the Files Go
RetroArch
The system directory, which you can confirm under Settings > Directory > System/BIOS:
| Platform | System directory |
|---|---|
| Windows | RetroArch\system\ |
| Linux | ~/.config/retroarch/system/ |
| macOS | ~/Library/Application Support/RetroArch/system/ |
| Android | /storage/emulated/0/RetroArch/system/ |
| Steam Deck (Flatpak) | ~/.var/app/org.libretro.RetroArch/config/retroarch/system/ |
Beetle Saturn and Yabause read from the root of that folder. Kronos is the odd one: it looks in system/kronos/saturn_bios.bin first, then falls back to system/saturn_bios.bin, then system/sega_101.bin, then system/mpr-17933.bin. So a Beetle setup already satisfies Kronos, but a Kronos-only setup with the file inside kronos/ does not satisfy Beetle. Keep the two Beetle files at the root and you cover every core.
After loading a core, Quick Menu > Information > Core Information shows each file as Present or Missing with its hash. That is where you find out whether you have the v1.00 or v1.01 Japanese image.
EmuDeck on Steam Deck
EmuDeck’s cheat sheet puts the Beetle files flat in Emulation/bios/, Kronos in Emulation/bios/kronos/saturn_bios.bin, and Yabause in Emulation/bios/saturn_bios.bin. Its BIOS checker reads the hashes above.
Linux handhelds
| Firmware | BIOS folder | Saturn core |
|---|---|---|
| muOS | MUOS/bios/ on the OS card | Yabause or YabaSanshiro |
| Knulli / Batocera | /userdata/bios/, flat | Beetle Saturn on capable chips, YabaSanshiro otherwise |
| ROCKNIX / ArkOS | roms/bios/ on the games card | YabaSanshiro |
| Stock Anbernic Linux | BIOS/ at the games card root | Yabause |
Saturn is a heavy target. On an RK3566 device like the RG35XX H it is playable for 2D games and nothing else; the Android devices below are where it runs properly.
How to Verify
Get-FileHash .\mpr-17933.bin -Algorithm MD5
md5sum mpr-17933.bin
Size first, then hash. A Saturn BIOS is 524,288 bytes exactly. A 2 MB file with a .ic1 name is a cartridge ROM, not the BIOS. If your hash does not match any of the three in the table, check the size; if the size is right, it is most likely a different revision that the saturn_bios.bin cores will still boot.
How to Dump the BIOS From Your Saturn
The BIOS sits at address 0x80000 in the Saturn’s memory map, 512 KB long, and homebrew can read it directly. The tool I use is Save Game Copier by slinga, on GitHub. Its Dumping Memory feature writes that region out to whatever storage it can reach.
How you run the homebrew depends on what your Saturn has:
- Optical drive emulator (MODE, Satiator, Fenrir). Load Save Game Copier from the ODE’s menu, dump, and the file lands on the ODE’s SD card. Cleanest route.
- SAROO cartridge. Its own menu writes the BIOS straight to the microSD card.
- Action Replay or Pseudo Saturn Kai cartridge. These let a stock Saturn boot a burned CD-R, so burn Save Game Copier to a disc, boot it, and dump to the cartridge’s save memory or a connected device.
- Desoldering the ROM and reading it in a programmer. It works and it is how the original dumps were made, but you are risking a board for a file the routes above produce in five minutes.
Pseudo Saturn Kai itself does not dump the BIOS. Its save manager dumps cartridge ROMs. It is the disc-boot step, not the dumper.
Which region you get depends on the console: a Japanese Saturn gives you a sega_101.bin-class file, an American or European one gives you the mpr-17933.bin image. For Beetle Saturn you want both, which means two consoles or a friend with the other region.
Common Problems
Kronos boots to nothing. No saturn_bios.bin in system/kronos/ or at the system root. Kronos does not switch to HLE by itself.
Beetle Saturn refuses a Japanese game. sega_101.bin missing. Beetle picks the BIOS by disc region and needs the matching file.
Yabause runs most games but a few black-screen. You are on the emulated BIOS. Add the real file.
Multi-disc game will not load from an .m3u. Yabause and YabaSanshiro need the real BIOS for .m3u playlists.
Set Language and Set Clock screens on every boot. Not a BIOS problem. The emulator’s internal backup RAM is being reset, usually because the save directory is not writable, or on real hardware the CR2032 is dead.
Saves made under one BIOS freeze under another. European and Japanese BIOS images handle backup RAM differently. Pick one BIOS per game and keep it.
Why No Download Links
The Saturn BIOS is Sega’s copyrighted code. Dumping it from a console you own takes minutes with homebrew that is free and open, and it produces a file you can hash and trust. The “Saturn BIOS pack” sites produce a zip of unknown origin and an installer you did not ask for.
FAQ
Is saturn_bios.bin the same as sega_101.bin?
No. saturn_bios.bin is the Japanese v1.00 image; sega_101.bin is v1.01. Both are real, both boot the Yabause-family cores, and Beetle Saturn only reads the second.
Which Saturn BIOS do I need for US games?
mpr-17933.bin for Beetle Saturn and Mednafen. For Kronos and Yabause, any Saturn BIOS renamed to saturn_bios.bin.
Does YabaSanshiro need a BIOS?
It runs without one, but compatibility drops and multi-disc sets fail. Use the real file.
Where does the Saturn BIOS go for Kronos?
system/kronos/saturn_bios.bin, with a fallback to the system root.
Can I dump the BIOS with a Pseudo Saturn Kai?
Not directly. The cart lets your Saturn boot a burned homebrew disc; Save Game Copier on that disc does the dumping.
Beetle Saturn core docs | Kronos core docs | Mednafen Saturn docs | Save Game Copier
Last verified: September 2026