Hard Real time:Hard real time systems are the ones in which critical deadlines are met strictly. Missing a deadline means failure of the system.
Ex: Mission critical systems like missile launching systems.
Firm Real time:If missing its deadline makes the result useless, but missing does
not cause serious damage
Soft Real Time:In Soft real time systems, occasional missing of deadlines (small delays) are acceptable and not considered as failure. Rather it is considered as performances degrade.
Ex: Cell phones