Real-time computer systems consist of hardware and software that is designed to guarantee a response to an event within very tight timing constraints. This type of system is often described as being deterministic. Modern PC systems running a standard operating system can often perform calculations and make decisions within a very short time. However as the operating system splits processor resources between a large number of other time varying background tasks, the response time cannot to an event cannot be accurately predicted, or repeated. In contrast real-time systems often consist of relatively simple hardware and software, but with a very high priority given to the main task, so that a response deadline is accurately met. Real-time systems are commonly used in safety critical control processes, therefore typical applications include: automotive safety, aerospace control and industrial automation.