A real-time operating system (RTOS) is a class of operating system intended for real-time applications. Such applications include embedded (programmable thermostats, household appliance controllers, mobile telephones), industrial robots, spacecraft, industrial control (e.g. SCADA), and scientific research equipment.
A RTOS facilitates the creation of a real-time system, but does not guarantee the finished product will be real-time; this requires correct development of the software. A RTOS does not necessarily have high throughput; rather, a RTOS provides facilities which, if used properly, guarantee deadlines can be met generally ("soft real-time") or deterministically ("hard real-time"). A RTOS will typically use specialized scheduling algorithms in order to provide the real-time developer with the tools necessary to produce deterministic behavior in the final system. A RTOS is valued more for how quickly and/or predictably it can respond to a particular event than for the given amount of work it can perform over time. Key factors in an RTOS are therefore minimal interrupt and thread switching latency.
A RTOS facilitates the creation of a real-time system, but does not guarantee the finished product will be real-time; this requires correct development of the software. A RTOS does not necessarily have high throughput; rather, a RTOS provides facilities which, if used properly, guarantee deadlines can be met generally ("soft real-time") or deterministically ("hard real-time"). A RTOS will typically use specialized scheduling algorithms in order to provide the real-time developer with the tools necessary to produce deterministic behavior in the final system. A RTOS is valued more for how quickly and/or predictably it can respond to a particular event than for the given amount of work it can perform over time. Key factors in an RTOS are therefore minimal interrupt and thread switching latency.
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Last Updated: Sep 2009
Last Updated: Sep 2009
What are Realtime Operating Systems RTOS?
A significant problem that multitasking systems must address is sharing data and hardware resources among multiple tasks. It is usually "unsafe" for two tasks to access the same specific data or hardware resource simultaneously. ("Unsafe" means the results are inconsistent or unpredictable, particularly when one task is in the midst of changing a data collection. The view by another task is best done either before any change begins, or after changes are completely finished.)
General-purpose operating systems usually do not allow user programs to mask (disable) interrupts, because the user program could control the CPU for as long as it wished. Modern CPUs make the interrupt disable control bit (or instruction) inaccessible in user mode to allow operating systems to prevent user tasks from doing this. Many embedded systems and RTOSs, however, allow the application itself to run in kernel mode for greater system call efficiency and also to permit the application to have greater control of the operating environment without requiring OS intervention.
General-purpose operating systems usually do not allow user programs to mask (disable) interrupts, because the user program could control the CPU for as long as it wished. Modern CPUs make the interrupt disable control bit (or instruction) inaccessible in user mode to allow operating systems to prevent user tasks from doing this. Many embedded systems and RTOSs, however, allow the application itself to run in kernel mode for greater system call efficiency and also to permit the application to have greater control of the operating environment without requiring OS intervention.
