The XDK Debug BIOS, is an alternate BIOS created by Microsoft for Xbox gaming system. It is included in Debug Xbox consoles that are used by game software developers. It differs from a Retail BIOS by allowing the MicrosoftXDK to link with the Xbox while it is executing code and receive feedback. It also allows for the running of code not digitally signed by Microsoft, similar to a hacked Retail BIOS, since finalized code must be submitted to Microsoft for a key to run on unmodified Retail consoles.
The debug and retail BIOSes do not differ much, and as a result hackers have been able to create hacked debug BIOSes which can be run on any retail Xbox. Thus, any Xbox can be converted into a Development Xbox. By further studying the debug BIOS, hackers have gained the ability to modify any Xbox BIOS in a way which allows them to load it from the internal hard disk, and then boot it 'on the fly'. This hack has been of great significance to the Xbox community.