# fdsboot: Famicom Disk System boot ROM disassembly

> fdsboot is a 6502 disassembly of the Famicom Disk System boot ROM, split into disk I/O, PPU, joypad, timer, sound, interrupt and random-number routines with include files for the console and FDS registers. The ca65/ld65 build reassembles fdsboot.bin and compares its CRC with the original and with a second revision, 3DS and Wii VC builds, and GW and TWIN variants selected by assembler flags. It serves as a reference when disassembling Famicom Disk System titles.

- Type: Case study
- Targets: Firmware
- Category: Independent reconstruction cases
- Relationship: Independent reconstruction project
- Sources reviewed: 2026-11-09
- Added to the catalog: 2026-11-10
- Original resource: <https://gitlab.com/segaloco/fdsboot>
- Primary source: <https://gitlab.com/segaloco/fdsboot/-/blob/61707587905f2567650ae9a3e77c33c88905af62/README>
- Catalog page: <https://awesomerea.org/resources/fdsboot-case/>
- Record JSON: <https://awesomerea.org/resources/fdsboot-case/record.json>
- Chinese version: [简体中文](https://awesomerea.org/zh/resources/fdsboot-case/index.md)

## Requirements & limits

- **Prerequisites:** Needs the cc65 assembler and linker (ca65, ld65) with make, or plan9port mk.
- **Prerequisites:** The font and two data tables are extracted from the user's own boot ROM image with tools/extract.sh before building.
- **Limits:** Where the source commentary and the assembly differ, the assembly is authoritative.
- **License:** No licence file in the repository.

## Primary sources

1. <https://gitlab.com/segaloco/fdsboot/-/blob/61707587905f2567650ae9a3e77c33c88905af62/README>
2. <https://gitlab.com/segaloco/fdsboot/-/blob/61707587905f2567650ae9a3e77c33c88905af62/Makefile>
3. <https://gitlab.com/segaloco/fdsboot/-/blob/61707587905f2567650ae9a3e77c33c88905af62/.gitlab-ci.yml>
4. <https://gitlab.com/segaloco/fdsboot/-/blob/61707587905f2567650ae9a3e77c33c88905af62/tools/extract.sh>

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## About this entry

The description was reviewed against primary sources.
Original editorial content: MIT. Linked projects, papers and assets retain their own rights and licenses.