Its application-specific: i.e. A spacecraft that requires a thruster to be fired with accuracy of a few hundred milliseconds in two years time has mission/safe

Its application-specific: i.e. A spacecraft that requires a thruster to be fired with accuracy of a few hundred milliseconds in two years time has mission/safety critical timing requirements. Therefore this is hard-real-time Alternatively, a payroll that has to run at the end of every month will not cause people to miss payments if that deadline is missed by any relatively large amount of time (minutes/hours). The timing requirements are not mission critical at this point. They could be considered soft-realtime tho as there is still an upper bound to desired behaviour.