Multi-region discs?

[King M]

spotted this sonic cd beta on ebay

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewI...0&category=3644

claims to work on any region sega/mega cd unit. i'm guessing it's just a burned copy of one of the isos everyone has, but i'm curious why the seller would claim it plays on any region. any insight?

 

[ExCyber]

As far as I know, that can't be done on Sega/Mega CD. The seller is probably passing on bad secondhand information.

 

[Mask of Destiny]

There isn't any way to have a multi-region disc as far as I can tell. The Sega CD checks for the specific security code of that region at offset 0x200 on the disc. There is no way to have all three security codes on the disc and have them be recognized by the BIOS. The only potential way around this would be some exploit of the BIOS code, but I didn't see anything exploitable in my reverse engineering efforts. Of course, this doesn't mean such an exploitable bug doesn't exist.