Interesting article: “The Hidden Boot Code of the Xbox, or How to fit three bugs in 512 bytes of security code.”
Microsoft wanted to lock out both pirated games and unofficial games, so they built a chain of trust on the Xbox from the hardware to the execution of the game code. Only code authorized by Microsoft could run on the Xbox. The link between hardware and software in this chain of trust is the hidden “MCPX” boot ROM. The article discusses that ROM.
Lots of kindergarten security mistakes.