1. What is real time?

1.1 System and application specificities

A real-time application is one for which the time factor is the main constraint to be respected. The application has to deliver the right result, but if it's not delivered on time, it can't be validated. On the other hand, it's not a question of delivering the result as quickly as possible, but simply on time. The time scale relative to the time constraint varies from one application to another: it may be, for example, of the order of microseconds in radar control applications, but of the order of a few minutes for a chemical process control application. Real-time systems can also be referred to as embedded systems.

There are two types of time constraints:

• strict temporal...