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# Game & Watch - RetroBIOS

Type | libretro
Classification | pure_libretro
Source | https://github.com/libretro/gw-libretro
Upstream | http://www.madrigaldesign.it/sim/
Version | Git
Profiled | 2026-03-25
Cores | gw
Systems | handheld-electronic

Source analysis

content_format:

    - **extension:** .mgw
    - **archive_type:** tar v7 + bzip2
    - **decompression:** gwrom.c using bundled bzip2 library
    - **source_ref:** gwrom/gwrom.h:21-27

game_engine:

    - **language:** Lua (bundled lua 5.3)
    - **runtime:** gwlua (gwlua/)
    - **rendering:** retroluxury (retroluxury/)
    - **resolution:** 128x128 base, variable via gwlua_set_fb/gwlua_zoom

- filesystem_access: False
- system_directory_used: False

Technical notes

gw-libretro runs Game & Watch simulators converted from MADrigal's Pascal source code via pas2lua. Each game is a self-contained .mgw archive (bzip2 compressed tar v7) containing Lua scripts, sprites, and sound data.

retro_get_system_info (libretro.c:187-194) sets valid_extensions to "mgw", need_fullpath to false, and block_extract to false. The core reads content entirely from the retro_game_info buffer passed by the frontend.

retro_load_game (libretro.c:256-310) passes the content buffer to gwrom_init() which decompresses and parses the tar archive in memory. gwlua_create() then initializes the Lua VM from the archive entries.

The core never calls RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY, never opens files from the filesystem, and has no firmware or BIOS dependencies. All game data is bundled in the .mgw content files available from libretro's buildbot (bot.libretro.com/assets/cores/HandheldElectronicGame/).

No external BIOS or firmware files are needed.

No BIOS or firmware files required. Generated on 2026-03-25T14:56:43Z