How do Real Time Operating Systems work?

Question

I mean how and why are realtime OSes able to meet deadlines without ever missing them? Or is this just a myth (that they do not miss deadlines)? How are they different from any

Answer 1

What is important is realtime applications, not realtime OS. Usually realtime applications are predictable: many tests, inspections, WCET analysis, proofs, ... have been performed which show that deadlines are met in any specified situations.

It happens that RTOSes help doing this work (building the application and verifying its RT constraints). But I've seen realtime applications running on standard Linux, relying more on hardware horsepower than on OS design.