I stand corrected - I was thinking more of the "What do I do about a PC if I'm using Planet CNC or similar external motion controller?" question.

Whether or not LinuxCNC is truly a real-time operating system is one of those religious debates that go on endlessly. I'm happy to agree that, up to some reasonable pulse rate (and that rate is certainly sufficient for many machines) it works fine. I've been using it for more than three years with no observed problems. There are some random timing issues, which is why the LinuxCNC kit includes a latency tester which, in effect, measures how reliably the operating system can respond in "real-time" on some particular configuration of hardware but the answer is often hardware-dependent and there are some motherboards which just do not perform well. It's not related to raw CPU performance but even LCNC can't cope with some hardware. If you want to say that LCNC is truly real-time but is let down by the hardware, I can go with that