"In order to lock out both copied games as well as homebrew software, including the GNU/Linux operating system, Microsoft built a chain of trust on the Xbox reaching from the hardware to the execution of game code, in order to avoid the infiltration of code that has not been authorized by Microsoft. The link between hardware and software in this chain of trust is the hidden "MCPX" boot ROM. The principles, the implementations and the security vulnerabilities of this 512 bytes ROM will be discussed in this article. "

'How to fit 3 bugs in 512 bytes of security code' - Xbox