The Real Time Operating System
A real-time operating system (RTOS) is a multitasking operating system intended for
real-time applications. Real-time applications are ones that are subject to a “real-time”
constraint. Let’s use the anti-lock brakes on a car as an example of a real-time
computing system. The real-time constraint with brakes would be the short time the
brakes must be released to prevent the brakes from locking.
Such applications include embedded systems like programmable thermostats,
household appliance controllers, and mobile telephones. Other applications are
industrial robots, spacecraft, industrial control, and scientific research equipment.
A real time operating system facilitates the creation of a real-time system but does not
guarantee the final result will be real-time. This requires correct development of the
software. An RTOS does not necessarily have high through put. Rather, an RTOS
provides facilities which, if used properly, guarantee deadlines can be met general or
An 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 real time operating system is valued more for how quickly and/or
predictably it can respond to a particular even than for the given amount of work it can
perform over time. Key factors include minimal interrupt latency and a minimal thread
A system is said to be real-time is the correctness of an operation depends not only
upon the logical correctness of the operation but also upon the time at which it is
performed. The classical conception is that in a hard or immediate real-time system, the
completion of an operation after its deadline is considered useless. Ultimately this may
lead to a critical failure of the complete system. A soft real-time system on the other
hand will tolerate such lateness and may respond with decreased service quality.
For example, a car engine control system is a hard real-time system. That’s because a
delayed signal may cause engine failure or damage. Other examples of hard real-time
embedded systems also include medical systems like heart pacemakers and industrial
process controllers. Hard real-time operating systems are used when it is imperative
that an event is reacted to within a strict deadline.
A soft real time operating system could be like the software that maintains and updates
the flight plans for commercial airliners. These can operate to a latency of seconds. It
would not be possible to offer modern commercial air travel if these computations
could not reliably be performed in real time. Live audio-video systems are also usually
soft real-time; violation of constraints results in degraded quality, but the system can
continue to operate.
Most people don’t think about real-time operating systems, but they are really an
important part of your computer system.