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libretro/wiki/what-are-bios-files.md
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Abdessamad Derraz 602945faf0 feat: logos, build stamps and exact wording
- The installer says "Every file on the list is in place." where it
  said "Everything is in place.": a check covers the files the
  collection holds, and the required ones it lacks follow.
- The FAQ, first install, legal and home pages state only what the
  code shows (PlayStation 1 and Saturn run without a BIOS on some
  emulators, save files are never touched, records are added).
- MinUI and MyMinUI show their own boot logos, and the Android,
  Linux handheld and iPhone tiles show the Android robot, Tux and a
  plain device icon, each credited in sources.json.
- Each Markdown copy, llms.txt and llms-full.txt name the commit
  they were built from, version.json the current one, and the
  answering rules tell assistants to fetch a stale copy again.
- The deploy lists the pages whose words changed (digests.json) and
  posts them to IndexNow once the site is live.
2026-11-09 10:47:37 +01:00

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---
level: start
order: 10
---
# What is a BIOS?
A console has a small program inside it. It starts first, then starts the game.
This program is the **BIOS**, also called **firmware**.
<a class="rb-button rb-button-primary" href="../which-pack.md">Get the files</a>
An **emulator** is an app that acts like a console. For many consoles, it needs
a copy of the BIOS. That copy is a file: a **BIOS file**.
<!-- image: bios-chain -->
## How it works
1. Pick a game in the setup's menu.
2. The setup starts the emulator.
3. The emulator opens the BIOS file in the **BIOS folder**.
4. The game starts.
If step 3 fails, the screen says "BIOS missing" or stays black.
## Which consoles need one? { #do-i-need-one }
- **Yes:** PlayStation 2, Neo Geo, PC Engine CD and many home computers.
- **Most emulators:** PlayStation 1 and Saturn.
- **Better with it:** Dreamcast. Some games need it.
- **Usually not:** NES, Super Nintendo, Mega Drive, Game Boy and Game Boy
Advance.
- **Add-ons need their own:** the Famicom Disk System and the Mega CD.
Details: [Every console, one by one](../systems/index.md)
## The name must match
Most emulators look for one exact name, like `scph5501.bin`. A file with
another name is not found. A few, like DuckStation, read any name and check
what the file holds.
## The version must match
Two files can have the same name and different contents. One may be for Japan,
another for Europe.
Some setups check each file's **hash**, a fingerprint of its contents.
Batocera, Recalbox and EmuDeck report a version they do not expect.
## Can a game start without it?
Sometimes. Some emulators carry their own code in place of the BIOS. Some games
then glitch or do not start.
## Is it legal?
Laws differ by country. [Is it legal?](legal.md)
## Next steps
- [Get the files](../which-pack.md)
- [Words used on this site](glossary.md)