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RetroBIOS

Gearsystem

Gearsystem emulates Sega Master System, Sega Game Gear and Sega SG-1000. It reads 2 files, none of them required: it starts games without them.

About this profile
Detail Value
Type libretro
Classification Official port
Source https://github.com/drhelius/Gearsystem
Version 3.9.23-10-g215c22f, 10 commits after tag 3.9.23
Revision drhelius/Gearsystem@215c22f73d06
Profiled 2026-03-23
Profile YAML, JSON
Cores gearsystem
Systems Sega Master System, Sega Game Gear, Sega SG-1000
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 gearsystem
Platform details

  • mastersystem:

    • bios_filename: bios.sms
    • source_ref: src/Memory.cpp:238-243
    • note: Boot ROM loaded via LoadBootromSMS() -> LoadBootroom(path, false). Raw binary read, stored in m_pBootromSMS. Bank count computed as Pow2Ceil(size / 0x4000). Memory mapping controlled by port 3E bit 3.

  • gamegear:

    • bios_filename: bios.gg
    • source_ref: src/Memory.cpp:245-250
    • note: Boot ROM loaded via LoadBootromGG() -> LoadBootroom(path, true). Raw binary read, stored in m_pBootromGG. Same bank computation. Supports standard GG BIOS and Majesco 1KB variant.

  • sg1000:

    • bios_filename: none
    • note: No BIOS support. src/Memory.cpp:352-355 returns false from IsBootromEnabled() when IsSG1000() or IsGameGearInSMSMode() is true.
Technical notes

Gearsystem is a Sega Master System / Game Gear / SG-1000 emulator by Ignacio Sanchez (drhelius). No BIOS is required for normal operation.

The core supports optional boot ROMs for Master System and Game Gear, controlled by core options "gearsystem_bios_sms" and "gearsystem_bios_gg" (both disabled by default). Boot ROMs are loaded in load_bootroms() from the system directory with fixed filenames.

SG-1000 and Game Gear in SMS mode have no BIOS support. IsBootromEnabled() returns false for both cases.

When enabled, the boot ROM executes as on original hardware, which may cause invalid ROMs to lock or fail to boot entirely.

Files

Section titled “Files”

2 files: 0 required, 2 optional.

In this collection: 2 in repo and 0 missing.

Optional

Section titled “Optional”

bios.sms optional in repo

Source

bios.gg optional in repo

Source

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.