> Well, not exactly. I don't see why a hard real-time system can't
> say `nobody gets more than 80% of the CPU, ever.' It's the equivilant
> of putting a slower CPU in the machine.

JFW already answered this, but I'll throw in another two bits..

Hard real time is about guaranteed responses to events within a
specified time period... correctness depends not only on computing the
right answer, but also on computing it *before* (e.g.) the robot arm
punches through the wall and kills someone...

The real question is: 

Ok, with that scheme, nobody gets more than 80% of the CPU over *what
timescale*?  1s?  5s?  10ms?  100us?

That will provide a bound on exactly *how* hard the hard real-time
properties of the system are, and if those don't match your
requirements, it's time to find a new OS..

					- Bill