Would you be talking about the chip's architecture?
I recall the old Motorola 68x chips were "clear", in that you could (and did) load your OS onto the computer every boot-up, and that memory was loaded from "bottom-up", while the X86 "partitioned" memory usage and loaded memory above a certain address...
That's my best recollection of the differences..
At any rate, with my old 68x system, I could use a different OS, like Unix with my machine simply by booting a Unix disk, or replacing the OS chip on the motherboard with a Unix chip..
Is this the case here with Power PC?
And is it a Motorola descendent?
There is little information available on the processor, but if you follow this link to a preview on anandtech about the xbox 360 and click on the PPE link in the forth paragraph there is some interesting info on what may be used.
I surely would be. I don't hold myself out as any kind of expert, so I'd encourage you to use Google to clarify the differences between the Power PC chip and others.
The Power PC Chip does indeed have some Motorola parentage, along with IBM. I'm not sure who is currently manufacturing which versions.
The chip arcitecture of the power PC chip apparently doesn't have the buffer overflow issue that has been used in exploits against machines using X86 CPUs.