Systems used for many safety-critical applications must be real-time, such as for control of fly-by-wire aircraft, or anti-lock brakes, both of which demand immediate and accurate mechanical response.
Minicomputers, particularly in the 1970s onwards, when built into dedicated embedded systems such as DOG (Digital on-screen graphic) scanners, increased the need for low-latency priority-driven responses to important interactions with incoming data.
For example, Data General Business Basic could run in the foreground or background of RDOS and would introduce additional elements to the scheduling algorithm to make it more appropriate for people interacting via dumb terminals.
The possibility of deactivating other interrupts allowed for hard-coded loops with defined timing, and the low interrupt latency allowed the implementation of a real-time operating system, giving the user interface and the disk drives lower priority than the real-time thread.
Compared to these the programmable interrupt controller of the Intel CPUs (8086..80586) generates a very large latency and the Windows operating system is neither a real-time operating system nor does it allow a program to take over the CPU completely and use its own scheduler, without using native machine language and thus bypassing all interrupting Windows code.
This application area is one where real-time control offers genuine advantages in terms of process performance and safety.
Such strong guarantees are required of systems for which not reacting in a certain interval of time would cause great loss in some manner, especially damaging the surroundings physically or threatening human lives (although the strict definition is simply that missing the deadline constitutes failure of the system).
In some situations, these can guarantee hard real-time performance (for instance if the set of tasks and their priorities is known in advance).
Specific algorithms for scheduling such hard real-time tasks exist, like earliest deadline first, which, ignoring the overhead of context switching, is sufficient for system loads of less than 100%.
A common life analogy is standing in a line or queue waiting for the checkout in a grocery store.
Live audio digital signal processing requires both real-time operation and a sufficient limit to throughput delay so as to be tolerable to performers using stage monitors or in-ear monitors and not noticeable as lip sync error by the audience also directly watching the performers.
Tolerable limits to latency for live, real-time processing is a subject of investigation and debate, but is estimated to be between 6 and 20 milliseconds.
Conversely, once the hardware and software for an anti-lock braking system have been designed to meet its required deadlines, no further performance gains are obligatory or even useful.
In a real-time system, such as the FTSE 100 Index, a slow-down beyond limits would often be considered catastrophic in its application context.
The term "near real-time" or "nearly real-time" (NRT), in telecommunications and computing, refers to the time delay introduced, by automated data processing or network transmission, between the occurrence of an event and the use of the processed data, such as for display or feedback and control purposes.