DC custom BIOS

Hi there,

There is something I wanted to share before going any further in the bootROM/BIOS hacking for the Dreamcast. It is a modified BIOS base on the version 1.01d of the retail one.
Copy/paste of the readme:

  • Region free: boot GD/CD from any regions. The J/U/E flags as well as the area protection slots that reside in the AIP (A.K.A. IP.BIN) are now simply ignored.
  • No VGA flag check: no matter if the game supports the VGA output, the lets it boot. There are games that supports the VGA cable but for some reason the VGA flag in the AIP is not set. The use of a boot CD thus was needed. Now, you will never get the annoying “This game doesn’t support the AV cable that is currently connected to the main console” anymore.
  • Bootfile extent check: allow a game to boot even if its bootfile, more commonly called 1ST_READ.BIN, is not located on the outer part of the disc. I don’t know whether it can be of any use for people using discs. However, for the lucky owners of ODDE for Dreamcast, you can re-build games’ track 3 without any padding. For instance, with “Dreamkey 3.0 v1.001 (2001)(Sega)(PAL)(M8)[!]”, the track03.bin is ~1.10GB. Re-building the track (track03.iso) using the following command: mkisofs -C 0,45000 -V DREAMKEY3 -G IP.BIN -l -o track03.iso data will made the track03.iso way smaller (only ~93MB). Homebrews can also be rebuilt to GDI so that the 0GDTEXT.PVR texture shows up in the audio player 🙂
  • Display bootROM version: the current version of the bootROM appears in the up-right corner of the screen.

Download: jc-bootROM-v1.030.zip (get it from here)

I hope it will make the VGA freaks happy: no more boot disc required! (Except for some games but no worries, I’m going tackles them down soon 🙂

12 replies on “DC custom BIOS”

Y3eah i figured that might be, I’ve contacted a dude over at assemblergames about some bios chips. Hopefully he will get back to me soon.

He wanted to know if it was possible to flash the bios without mods. The answer is no.

Good job on that bios japanese_cake! Any chance you might document which modification does what? Also, DevKit intro?



The bios with the devkit intro is done except that the holly check does not pass for the moment. I’ve to work on that when I have more time. About the modifications, I can give you more details but I would prefer doing that via email if you don’t mind. Just send me an email 😉

Hey, Quick question, I just received my new bios chips in the mail, and i remembered that I had previously read that San Francisco Rush 2049 (PAL) doesn’t work with some custom bios’, Is it the same with his bios?

Hi your “VGA BIOS” sounds great! And frankly I’m getting a little tired of the devkit intro I currently have. So it’s nice that you have both kinds available 😀

Does this produce any errors if I try to boot a 240p game, with regular RGB-cables? I’d still want that feature, but easier VGA-compatibility is definitely a huge plus 🙂

In my Dreamcasts I removed the original BIOS and installed a pre-flashed one instead. Can this chip be reflashed, or do I need to install another one with your BIOS?



Hi Martin,

So basically calling the custom BIOS “VGA BIOS” is a bit misleading because the BIOS does not enforce VGA output. It just disables the VGA flag check because some games are technically VGA compatible but some reasons the VGA flag is not set.

The only known issue with this BIOS is that it does not allow bleemcast disc (not the beta version, the retail ones) to boot. It should be fine for your 240p setup 😉

If you have a new BIOS chip installed it probably supports write operation. Just use the BIOS Flasher app from dreamshell to check that out.

Maybe it does. But it will probably require one of the legs to be pulled low or high to enable write mode. I don’t have much time on my hands the next few weeks, but I hope I can look into it after that 🙂

Strange that it doesn’t work with Bleemcast, but having never used it I don’t think that will be an issue 🙂

Thank you.


Leave a Reply