> One higher instance must be present to control shared resources like RAM, bus
> access etc. On modern processors this may be done in silicon (hypervisor), but
> on G4 or G5 this would be done in software.

The PPC970 CPUs themselves have hypervisor capability (inherited from POWER4 which was IBM's first hypervisor-enabled CPU) but which is disabled on Apple's G5 machines via OpenFirmware (and cannot be re-enabled). I suspect this may have been due to a deal with IBM so that IBM's server customers wouldn't even consider buying cheaper Xserve G5 instead.