A clarification of what 'real time' actually means in technical contexts, contrasted with its colloquial usage. A real-time system's correctness depends not just on logical results but on when those results are produced — missing timing constraints constitutes failure. The key property is determinism: low variance in operation timing. Classic RTOSes exhibit very low variance and are highly deterministic, while Linux generally has higher variance. The 'brute force' approach of overprovisioning CPU power can mask nondeterminism but isn't always practical. Real time means predictable and timely enough for the application's needs — not simply fast.
