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In computer science, real-time computing (RTC) is the study of hardware and software systems which are subject to a "real-time constraint"—i.e., operational deadlines from event to system response. By contrast, a non-real-time system is one for which there is no deadline, even if fast response or high performance is desired or even preferred. The needs of real-time software are often addressed in the context of real-time operating systems, and synchronous programming languages, which provide frameworks on which to build real-time application software. Computer science, or computing science, is the study of the theoretical foundations of information and computation and their implementation and application in computer systems. ...
RTC is an initialism that may refer to: Road Traffic Collision formerly called Road Traffic Accident Rail traffic controller, a person who oversees the movement of trains and controls railway signals. ...
Computer hardware is the physical part of a computer, including the digital circuitry, as distinguished from the computer software that executes within the hardware. ...
It has been suggested that this article or section be merged with Computer program. ...
A real-time operating system (RTOS) is a class of operating system intended for real-time applications. ...
A synchronous programming language is a programming language optimized for programming reactive systems, systems that are often interrupted and must respond quickly. ...
A real time system may be one where its application can be considered (within context) to be mission critical. The anti-lock brakes on a car are a simple example of a real-time computing system — the real-time constraint in this system is the short time in which the brakes must be released to prevent the wheel from locking. Real-time computations can be said to have failed if they are not completed before their deadline, where their deadline is relative to an event. A real-time deadline must be met, regardless of system load. // Summary Mission Critical is an adventure game released in 1995 by Legend Entertainment. ...
An anti-lock braking system (commonly known as ABS, from the German name Antiblockiersystem given to it by its inventors at Bosch) is a system on motor vehicles which prevents the wheels from locking while braking. ...
The system load is a UNIX computing term that describes the amount of work that a computer system is doing. ...
History
The term real time derives from its use in early simulation. While current usage implies that a computation that is 'fast enough' is real time, originally it referred to a simulation that proceeded at a rate that matched that of the real process it was simulating. Analog computers, especially, were often capable of simulating much faster than real time, a situation that could be just as dangerous as a slow simulation if it were not also recognized and accounted for. Look up simulation in Wiktionary, the free dictionary. ...
An analog computer (American English) or analogue computer (British English) is a form of computer using electronic or mechanical phenomena to model the problem being solved by using one kind of physical quantity to represent another. ...
Once when the MOS Technology 6502 (used in the Commodore 64 and Apple II), and later when the Motorola 68000 (used in the Macintosh, Atari ST, and Commodore Amiga) were popular, anybody could use their home computer as a real-time system. The possibility to deactivate other interrupts allowed for hard-coded loops with defined timing, 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[citation needed]. The Motorola 68000 and subsequent family members (68010, 68020 etc) also became popular with manufacturers of industrial control systems thanks to this facility. This application area is one in which real-time control offers genuine advantages in terms of process performance and safety. The MOS Technology 6502 is an 8-bit microprocessor that was designed by Chuck Peddle for MOS Technology in 1975. ...
The Commodore 64 is the best-selling single personal computer model of all time. ...
The Apple II was one of the most popular personal computers of the 1980s. ...
The Motorola 68000 is a 32-bit CISC microprocessor from Motorola. ...
The Macintosh 128K, the first Macintosh computer, introduced in 1984, upgraded to a 512K Fat Mac The Macintosh, or Mac, is a line of personal computers designed, developed, manufactured, and marketed by Apple. ...
The Atari 520ST Atari 1040STF with SC1224 color monitor The Atari ST is a home/personal computer that was commercially popular from 1985 to the early 1990s. ...
Amiga is the name of a range of home/personal computers using the Motorola 68000 processor family, whose development started in 1982. ...
Interrupt latency is the time between the generation of an interrupt by a device and the servicing of the device which generated the interrupt. ...
The Motorola 68000 is a 32-bit CISC microprocessor from Motorola. ...
Hard and Soft real time systems A system is said to be real-time if 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 (e.g., dropping frames while displaying a video).
Hard real-time systems are typically found interacting at a low level with physical hardware, in embedded systems. For example, a car engine control 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 heart pacemakers and industrial process controllers. It has been suggested that Embedded System Design in an FPGA be merged into this article or section. ...
Karl Benzs Velo (vélo means bicycle in French) model (1894) - entered into the first automobile race 2005 MINI Cooper S. An automobile (also motor car or simply car) is a wheeled passenger vehicle that carries its own motor. ...
An engine is something that produces an effect from a given input. ...
A pacemaker A pacemaker (or artificial pacemaker, so as not to be confused with the hearts natural pacemaker) is a medical device designed to regulate the beating of the heart. ...
Hard real-time systems are used when it is imperative that an event is reacted to within a strict deadline. Usually such strong guarantees are required of systems for which not reacting in a certain window of time would cause great loss in some manner, such as physically damaging the surroundings or threatening human lives; although the strict definition is simply that missing the deadline constitutes complete failure of the system. Systems that always have hard real-time constraints (due to the potentially severe outcome of missing a deadline) include nuclear power stations and car airbags. In the context of multitasking systems the scheduling policy is normally priority driven pre-emptive schedulers. Other scheduling algorithms include Earliest Deadline First, which, ignoring the overhead of context switching, is sufficient for system loads of less than 100%.[citation needed] Multitasking may refer to any of the following: Computer multitasking - the apparent simultaneous performance of two or more tasks by a computers central processing unit. ...
Earliest deadline first (EDF) scheduling is a dynamic scheduling principle used in real-time operating systems. ...
A context switch is the computing process of storing and restoring the state (context) of a CPU such that multiple processes can share a single CPU resource. ...
New overlay scheduling systems, such as an Adaptive Partition Scheduler assist in managing large systems with a mixture of hard real-time and non real-time applications. Adaptive Partition Schedulers are a relatively new type of partition scheduler, pioneered with the most recent version of the QNX operating system. ...
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 changing situations. Example: 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. An Airbus A380 of Emirates Airline An airline provides air transport services for passengers or freight. ...
It is important to note that hard versus soft real-time does not necessarily relate to the length of time available. A machine may overheat if a processor does not turn on cooling within 15 minutes (hard real-time). On the other hand, a network interface card may lose buffered data if it is not read within a fraction of a second, but the data can be resent over the network if needed, without affecting a critical operation, perhaps without a delay noticeable to the user. A transitional network card with both BNC Thinnet (left) and Twisted pair (right) connectors. ...
Real time and high performance Real-time computing is sometimes misunderstood to be high performance computing, but this is not always the case. For example, a massive supercomputer running a scientific simulation may offer impressive performance, yet it is not executing a real-time computation. Conversely, once the hardware and software for an anti-lock braking system has been designed to meet its required deadlines, no further performance gains are necessary. Furthermore, if a network server is highly loaded with network traffic, its response time may be slower but will (in most cases) still succeed. Hence, such a network server would not be considered an RTC system: temporal failures (delays, time-outs, etc.) are typically small and compartmentalized but are not catastrophic failures. In an RTC system, a slow-down beyond limits would often be considered catastrophic in its application context. The field of high performance computing (HPC) comprises computing applications on (parallel) supercomputers and computer clusters. ...
A supercomputer is a computer that leads the world in terms of processing capacity, particularly speed of calculation, at the time of its introduction. ...
Some kinds of software, such as many chess-playing programs, can fall into either category. For instance, a chess program designed to play in a tournament with a clock will need to decide on a move before a certain deadline or lose the game, and is therefore a real-time computation, but a chess program that is allowed to run indefinitely before moving is not. In both of these cases, however, high performance is desirable: the more work a tournament chess program can do in the allotted time, the better its moves will be, and the faster an unconstrained chess program runs, the sooner it will be able to move. This example also illustrates the essential difference between real-time computations and other computations: if the tournament chess program does not make a decision about its next move in its allotted time it loses the game—i.e., it fails as a real-time computation—while in the other scenario, meeting the deadline is assumed not to be necessary. 1990s Pressure-sensory Chess Computer with LCD screen The idea of creating a chess-playing machine dates back to the eighteenth century. ...
Design methods Several methods exist to aid the design of real-time systems, an example of which is MASCOT, an old but very successful method which represents the concurrent structure of the system. Other examples are HOOD, Real-Time UML, the Ravenscar profile and Real-Time Java. Wikiquote has a collection of quotations related to: Edsger Dijkstra The Dining Philosophers, a classic problem involving concurrency and shared resources In computer science, concurrency is a property of systems which consist of computations that execute overlapped in time, and which may permit the sharing of common resources between those...
HOOD (Hierarchical Object Oriented Design) is a detailed software design method. ...
The Ravenscar profile is a subset of the Ada tasking features. ...
RTSJ is an acronym that stands for Real-Time Specification for Java. ...
Key people - David Dill
- Rajeev Alur
- Costas Courcourbetis
- Alan Burns
Professor Alan Burns (currently beardless) Professor Alan Burns is currently the head of the University of York Computer Science Department. ...
See also A real-time operating system (RTOS) is a class of operating system intended for real-time applications. ...
A synchronous programming language is a programming language optimized for programming reactive systems, systems that are often interrupted and must respond quickly. ...
To meet Wikipedias quality standards, this article or section may require cleanup. ...
High frequency computing is a class of computer programming applications that relate to the processing of high-volume data streams, usually in real-time or near real-time. ...
// Background DSOS(tm) was a real-time operating system (some would say an operating system kernel) developed by Texas Instruments Geophysical Services division (GSI) in the mid-1970s. ...
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