06-09-2017, 04:10 PM
A real-time operating system (RTOS) is a computer environment that reacts to input in a specific period of time. A real-time deadline may be so small that the system's reaction appears instantaneous. The term real-time computing has also been used, however, to describe the slow real-time output that has a longer but fixed time limit.
Learning the difference between real-time and standard operating systems is as easy as imagining yourself in a computer game. Each of the actions you take in the game is like a program that runs in that environment. A game that has a real-time operating system for your environment can feel like an extension of your body because you can count on a specific "delay time": the time between your request for action and the remarkable execution of your request by Computer. However, a standard operating system may feel disconnected because the delay time is not reliable. To achieve the reliability of time, real-time programs and their operating system environment must prioritize the update of deadlines before anything else. In the game example, this could result in missing frames or lower visual quality when reaction time and visual effects conflict.
An RTOS must respond in a timely manner to the changes, but that does not necessarily mean that an RTOS can handle a large volume of data. In fact, in an RTOS, the small response times are valued much higher than the calculation power, or data rate. Sometimes an RTOS will even have to drop the data to make sure it meets its strict deadlines. In essence, that gives us a perfect definition: an RTOS is an operating system designed to meet strict deadlines. Beyond that definition, there are few requirements as to what an RTOS should be, or what features it should have. Some implementations of RTOS are very complete and very robust, while other implementations are very simple and suitable for a single purpose.
An RTOS can be event driven or time-shared. An event-driven RTOS is a system that changes state only in response to an incoming event. Time-sharing RTOS is a system that changes status as a function of time.