Optional Genesis BIOS - What do they actually "do"?

GenesisPlus GX core

  • sk.bin (Sonic & Knuckles ROM)
  • sk2chip.bin (Sonic & Knuckles UPMEM ROM)
  • areplay.bin (Action Replay ROM)
  • ggenie.bin (Game Genie ROM)

Ok, so clearly it’s easy to see what these ARE. The sk ones are related to lock-on features, and the other 2 are cheat devices…

But what’s the actual USE?

I mean, we have the Sonic 1/2/3 +S&K roms as games, and cheats work directly through the emulator…

So what do these actually DO? Like what’s the benefit of having them?

It’s just there to digitally preserve ‘Lock-On-Technology’ for the Genesis.

There’s no real benefit to normal end-users but I can think of two uses for really dedicated gamers.

You can simulate the experience of entering codes one character at a time into a Game Genie menu and then playing Sonic the Hedgehog with infinite rings.

This is a passage I got from Sega Retro regarding connecting Sonic & Knuckles with a non-Sonic game.

When a non-Sonic game is plugged in, the result is a single stage of Blue Sphere, produced randomly from information in the inserted cartridge’s ROM header, along with the stage’s ‘code’ for use in the full Blue Sphere. If Locked-On with a game larger than 2 Megabytes, it will boot to Sonic & Knuckles on real hardware, as the Sonic & Knuckles cart’s mapper will map the last 2MB of the locked-on ROM instead of the first 2MB. Locking-On with a game that uses a battery pack erases saved games. Most games made after Sonic & Knuckles was released are larger than 2MB and thus will not work with its lock-on feature. There are only a few games made before Sonic & Knuckles that do not work, such as Phantasy Star IV: The End of the Millennium & Super Street Fighter II: The New Challengers.

You can play random Blue Sphere levels, if that’s your thing.


So then what would be the difference between the 2 lock on bios? or are both of them necessary for that function?

And how would you start the ‘system’ so it loads the game genie followed by the games with the codes?

You need both sk.bin and sk2chip.bin for Sonic & Knuckles lock-on.

The game genie procedure would be like this.

  1. Have ggenie.bin in RetroArch’s System Directory.
  2. Load Sonic the Hedgehog with the Genesis Plus GX core.
  3. Set the Cartridge lock-on core option to game genie
  4. The core will automatically reset and boot you to the game genie menu.
  5. Enter code
  6. Press start to play Sonic the Hedgehog with the code.
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Thanks! That’s pretty badass. Wish we could get that for the NES - I’m pretty sure I still have my cheatbook somewhere… haha.

Anyway I’m gonna get that setup for the hell of it - I just wasn’t sure there was much point in me tracking down the BIOS for it.

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Where exactly would you find these? Do I need to dump the roms myself?

There is a way to enter Game Genie Codes for NES games afaik.

That is the legally preferred method.

This was almost 6 years ago, so It’s likely more options are available now. At the time though I wasn’t aware of a core option to allow GG code entry via the original interface of the cartridge - most cores/emulators have some kind of GG code entry, but I was referring more to the experience.