Hi All,
Keith is right, there is at least one realtime Linux distro, the one I am thinking of is Ubuntu Realtime. As Keith says it sticks to the business at hand,
if you nominate your CNC software as business that's what it does. Despite its billing its not in fact a real 'realtime' OS.

The genuine contenders for realtime OS have to guarantee a response time and there is a very specific technical standard to which it must comply
and is required for any number of important systems; medical, automotive, aerospace.... If you search FreeRTOS you will find more info.
Yes as the name implies you can have a genuine realtime OS for free!!! Downside is at least from our point of view is that it doesn't apply
to PC type OS's. If you want a realtime scheduler for a microcontroller running the ABS system in a car, one that has documented garantees
you're in luck.

Craig