Skip to content
RetroBIOS

Beetle Saturn

Beetle Saturn emulates Sega Saturn and Sega ST-V. It picks the BIOS for your game's region: sega_101.bin (Japan and Asia (NTSC)), mpr-17933.bin (North America, Europe, Oceania and 4 more), epr-20091.ic8 (Japan and Asia (NTSC)), epr-17952a.ic8 (North America, Brazil and Latin America) or epr-17954a.ic8 (Europe, South Korea and Asia (PAL)). The 5 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/beetle-saturn-libretro
Upstream https://mednafen.github.io/
Version v1.32.1, stated in libretro.c
Revision libretro/beetle-saturn-libretro@30f4c12072d2
Profiled 2026-10-05
Profile YAML, JSON
Cores mednafen_saturn, beetle-saturn
Systems Sega Saturn, Sega ST-V
Core ID mednafen_saturn_libretro
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 beetle_saturn
Technical notes

Libretro port of Mednafen's Saturn emulation module, converted to C and reporting v1.32.1 (libretro.c:58). Every firmware file is read from the system directory: MDFN_MakeFName joins retro_base_directory and the bare name for MDFNMKF_FIRMWARE (libretro.c:2347-2348), and the BIOS path is built the same way (mednafen/ss/ss.c:1868-1870).

Region comes from the disc header and the region table of mednafen/ss/db.c (libretro.c:1113-1115) and can be forced by the beetle_saturn_region option (libretro.c:454-476, libretro.c:1119-1120). With no content loaded the region defaults to North America (libretro.c:1069, libretro.c:1266-1267). The BIOS filename is hard-coded per region (mednafen/ss/ss.c:1846-1849): sega_101.bin for Japan and Asia NTSC, mpr-17933.bin for every other area. The file must be exactly 524288 bytes and InitCommon returns false when it is absent, of another size or short on read (mednafen/ss/ss.c:1944-1948, mednafen/ss/ss.c:1962-1985). The sha256 of the loaded image is kept only to refuse a save state made under another BIOS (mednafen/ss/ss.c:1989, mednafen/ss/ss.c:2584-2603). ss.bios_sanity answers true (mednafen/settings.c:50-51) but nothing in the port reads it: the name and hash table that upstream checks under that setting is not carried over.

The cartridge is chosen by the game table of mednafen/ss/db.c or by the beetle_saturn_cart option (libretro.c:478-496, libretro.c:1123-1124). The KOF95 and Ultraman ROM carts are opened from the system directory under the names of mednafen/settings.c:62-65 (mednafen/ss/cart.c:197-216). An absent file leaves the cart slot on the dummy handlers and the load goes on (mednafen/ss/cart.c:209).

ST-V content is a game ZIP or a bare ROM matched against the ST-V game table (libretro.c:1173-1193, libretro.c:1227-1247). The cabinet region of the matched game selects one of three ST-V BIOS images (mednafen/ss/ss.c:1830-1844), and the beetle_saturn_region option is not applied on that path (libretro.c:1183, libretro.c:1241). The image is read as a bare file from the system directory or, when that file is absent, as the member of the same name in stvbios.zip there, matched without regard to case (mednafen/ss/ss.c:1876-1950, zip_reader.c:350-357). Either form may be 131072 or 524288 bytes (mednafen/ss/ss.c:1912-1913, mednafen/ss/ss.c:1963).

The Video CD Card is driven through the CD block. With the beetle_saturn_mpeg_card option enabled (libretro.c:544-552, default disabled), CDB_Init opens mpeg_card.bin in the system directory and MPEG_Init keeps up to 0x80000 bytes of it (mednafen/settings.c:52-53, mednafen/settings.c:68-69, mednafen/ss/cdb.c:1316-1333, mednafen/ss/mpeg.c:580-607). A loaded image makes the card authenticate (mednafen/ss/mpeg.c:867-875), and the BIOS then reads the Video CD player program out of it with command 0xE2 (mednafen/ss/cdb.c:2924-2971, mednafen/ss/mpeg.c:839-859).

No setting names a file for the bootable ROM cart: ss.cart.bootrom_path has no value in the port (mednafen/ss/cart.c:242-262, mednafen/settings.c:60-71).

Files

Section titled “Files”

10 files. One of 5 is required, for your games' region. 5 are optional.

By kind: 9 BIOS and 1 BIOS ZIPs.

In this collection: 10 in repo and 0 missing.

Required

Section titled “Required”
FileStatus

sega_101.bin

  • System: Sega Saturn
  • Saturn BIOS v1.01 (Japan), loaded for the Japan and Asia NTSC areas. The port checks the size only. The sha256 is the value upstream Mednafen 1.32.1 holds for this filename in its ss.bios_sanity table (src/ss/ss.cpp, BIOSDB).
Hashes, validation and source
required for Sega Saturn in repo Region: Japan and Asia (NTSC)

mpr-17933.bin

  • System: Sega Saturn
  • Saturn BIOS v1.00a (North America and Europe), loaded for every area other than Japan and Asia NTSC, and when no content is loaded. Disc area E maps to EU_PAL and the code has no Oceania area (disc.c:162-165). The port checks the size only. The sha256 is the value upstream Mednafen 1.32.1 holds for this filename in its ss.bios_sanity table (src/ss/ss.cpp, BIOSDB).
Hashes, validation and source
required for Sega Saturn in repo Region: North America, Europe, Oceania, South Korea, Asia (PAL), Brazil and Latin America

epr-20091.ic8

  • System: Sega ST-V
  • ST-V BIOS for Japan and Asia NTSC cabinets. Read from stvbios.zip when the bare file is absent.
Validation and source
required for Sega ST-V in repo Region: Japan and Asia (NTSC)

epr-17952a.ic8

  • System: Sega ST-V
  • ST-V BIOS for North America and Central and South America cabinets. Read from stvbios.zip when the bare file is absent.
Validation and source
required for Sega ST-V in repo Region: North America, Brazil and Latin America

epr-17954a.ic8

  • System: Sega ST-V
  • ST-V BIOS for every other cabinet region. Read from stvbios.zip when the bare file is absent.
Validation and source
required for Sega ST-V in repo Region: Europe, South Korea and Asia (PAL)

Optional

Section titled “Optional”
FileContentsStatus

mpr-18811-mx.ic1

  • System: Sega Saturn
  • King of Fighters '95 ROM cart. Selected by the game table for MK-81088 and T-3101G or by the beetle_saturn_cart option. The first 0x200000 bytes are read. A shorter file installs a zeroed cart, an absent file leaves the slot empty.
Validation and source
-in repo

mpr-19367-mx.ic1

  • System: Sega Saturn
  • Ultraman: Hikari no Kyojin Densetsu ROM cart. Selected by the game table for T-13308G or by the beetle_saturn_cart option. The first 0x200000 bytes are read. A shorter file installs a zeroed cart, an absent file leaves the slot empty.
Validation and source
-in repo

stvbios.zip

ST-V BIOS archive

  • System: Sega ST-V
  • Opened only when the bare ST-V BIOS file for the cabinet region is absent. The member of the same name is matched without regard to case and must be 131072 or 524288 bytes. No hash is checked.
Source and 3 members
  • epr-20091.ic8: Japan and Asia NTSC
  • epr-17952a.ic8: North America and Central and South America
  • epr-17954a.ic8: Europe and every other region
3in repo BIOS ZIP

mpeg_card.bin

  • System: Sega Saturn
  • Video CD Card program ROM, opened when beetle_saturn_mpeg_card is enabled. The card carries a 512 KiB mask ROM. The core keeps at most 0x80000 bytes, pads a shorter image with zeros and checks nothing else. A loaded image makes the card authenticate. Command 0xE2 then copies the Video CD player program out of it, from the offset its first four bytes give plus 8, so an image of the wrong bytes authenticates but runs no player. Without it the card answers commands but does not authenticate.
Source
-in repo

satar4mp.bin

  • System: Sega Saturn
  • Action Replay 4M Plus firmware. The first 0x40000 bytes are read as big-endian words and a shorter file leaves the cart slot empty. No hash is checked. Unfinished in source (mednafen/ss/cart/ar4mp.c:22-24), needs CPU UBC emulation. Neither the beetle_saturn_cart option (libretro.c:478-496) nor the game table of mednafen/ss/db.c yields CART_AR4MP, so the case is not reached.
Validation and source
-in repo

Proof

Section titled “Proof”

Real runs that back this page (how they are made):

  • issue 85: with mpeg_card.bin and sega_101.bin, it gives no verdict (40 records).
  • issue 85: Video CD play, pause, stop and play again work (records 1, 2).
  • issue 85: next and previous track work on a three-track Video CD (record).
  • issue 85: the 704x480 menu still of Super Gamer No. 5 shows (record).
  • issue 85: the Lunar opening movie plays with sound (record).
  • issue 85: video and audio identical with and without the patch, card off and on, on 20 discs (95 records).

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.