Talk:Real-time computing

I would like to ask how does the real time operating system achieve the task in real time.How does it make sure that the given task is finished in the given amount of time.

Different RTOSs may do different things when a task does not complete in its alloted time (e.g., kill it and log an error, abort it this time and raise its priority for the next time, kill less critical tasks). In some cases they may do different things for different tasks (e.g., a flight critical task may be allowed to complete even if it runs over its alloted time, but non-flight critical tasks get killed to give the flight critical ones more time in the future). These are usually designer/programmer decisions and the RTOS must be properly configured to meet the system requirements.

But sometimes the RTOS doesn't even get a say in the matter, if the task doesn't complete in the alloted time it will never complete due to external "real world" events. The best example I ever heard of this was someone's description of a real time data collection computer they were working on that came up in a conference on design methodologies: "I don't think you understand what I mean when I say real time system. The system I am working on is attached at one end of a one meter long steel rod, at the other end of which is a nuclear bomb. It begins collecting data and transmitting it over a high speed link to another computer just before detonation. This system MUST complete all tasks before the radiation from the explosion destroys the processor. That is what I mean by real time system." That is an example of a true hard real time system. -- RTC 00:20 Apr 24, 2003 (UTC)