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# fixNES - RetroBIOS

Type | libretro
Classification | official_port
Source | https://github.com/libretro/fixNES
Upstream | https://github.com/FIX94/fixNES
Version | Alpha v1.3.1
Profiled | 2026-03-23
Cores | fixnes
Systems | nintendo-nes, nintendo-fds

Technical notes

fixNES is an NES/Famicom emulator by FIX94 (same author as fixGB).

FDS games require disksys.rom (8192 bytes) in the system directory. mapperInitFDS() in mapper.c:87-110 opens the file, validates exact size 0x2000, reads into fdsBIOS[]. Returns false if missing or wrong size. No hash validation.

Regular NES/NSF games need no BIOS.

No other system files loaded. system_dir accessed only for disksys.rom (libretro/libretro.c:277-285, doOpenFDSBIOS).

1 files | 1 required, 0 optional | 1 in repo, 0 missing

`disksys.rom` -required, both : Family Computer Disk System BIOS

- System: nintendo-fds
- Size: 8.0 KB
- Validation: size
- Source: `mapper.c:87-110 (mapperInitFDS), libretro/libretro.c:277-285 (doOpenFDSBIOS)`
- Platforms: batocera, emudeck, lakka, recalbox, retroarch, retrobat, retrodeck, retropie

Generated on 2026-03-25T14:56:43Z