Real-time computing
Real-time computing is the subject of hardware and software systems which are subject to constraints in time. Some kinds of software, such as many chess-playing programss, are allowed as much time as needed to perform a computation such as the next chess move. Web servers are an example of software that people work hard to optimize for performance, yet performance problems rarely incur any serious penalty.A distinction can be made between those systems which will suffer a critical failure if time constraints are violated (hard or immediate real-time), and those which will not (soft real-time).
Hard real-time systems are typically found interacting at a low level with physical hardware, in embedded systems. For example, a car's engine management system is a hard real-time system because a delayed signal may cause engine failure or damage. Other examples of hard real-time embedded systems include medical systems such as pacemakerss and industrial process controllers.
Soft real-time systems are typically those used where there is some issue of concurrent access and the need to keep a number of connected systems up to date with a changing situation on the ground. An example would be 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 typically soft real-time; violation of constraints results in degraded quality, but the system can continue to operate.
The needs of real-time software are often addressed with the use of real-time operating systems, which provide a framework upon which to build real-time application software.
