As designers piece together the requirements for each new project, real-time performance is one of the early considerations. OS vendors use terms like “hard” and “soft” to describe the real-time operation of their systems. Hard real-time embedded systems are scheduled so tasks are guaranteed to start within a precise length of time from an external event. Hard real-time embedded systems are deterministic. Soft real-time systems generally list the average length of time to start the routine, but there is a small probability that the maximum time can be much longer. Mission-critical applications must be deterministic. For example, industrial actuators, airbag controllers, and even arcade games must react in a known time. Soft real-time applications usually respond within a few seconds but an occasional slow response is not critical.