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A key characteristic of an RTOS is the level of its consistency concerning the amount of time it takes to accept and complete an application's task;

The fundamental difference is that the timing of RTOS tasks must be deterministic. If it is not there are either undesirable consequences (i.e. Soft realtime tasks like video playback) or system failure consequences (i.e Motor control signals). In contrast a general purpose OS has the primary goal of providing the best user experience possible. This means that timing will vary based on interpretation of need. For example interactive processes with the user on a terminal can have more CPU time than a background process. However, the OS makes no guarantees in contrast to the RTOS.