Scheduling is a central activity of a computer system, usually performed by the operating system. Fixed-priority scheduler is the polling-server in rate monotonic scheduling algorithm, which assigns higher priorities to tasks with shorter relative deadlines. It is intuitive to see that if every task's period is the same as its deadline, then the RM and DM scheduling algorithms are equivalent. Hard real-time systems have been defined as those containing processes that have deadlines that cannot be missed. Such deadlines have been termed hard: they must be met under all circumstances otherwise catastrophic system failure may result.