"We're taking an in-depth technical look at one of the Xbox 360's features, its hypervisor. The Xbox 360 contains a hypervisor to provide security for the system--good news for Microsoft, bad news for hackers, as Microsoft has included it as part of its plans for a hack-proof 360. What are the implications of this for gamers and for those who wish to experiment with their console?

Firstly, a look at how the processor executes code on the 360. The Xbox 360's CPU is based around the PowerPC architecture, which is well-suited to virtualisation. The hypervisor is a program on the system which can provide the operating system with virtual hardware or limit its access to memory, so a program running on top of a hypervisor thinks it is running inside a single virtual machine and talking directly to the hardware, rather than within another operating system.

On the Xbox 360, the hypervisor program is the bottom line, running in kernel mode (which means it has unlimited access to the system's hardware). The operating system runs on top of the hypervisor in user mode, and its access is meted out by the hypervisor. This means that the hypervisor can emulate the original Xbox without the 360's operating system being involved." [more]