The term real-time ( English real-time ) characterizes the operation of information technology systems can deliver the specific outcomes reliably within a predetermined time, for example in a fixed time frame.
The definition of the standard DIN 44300 (information processing), part 9 (processing sequences), which has since been replaced by DIN ISO / IEC 2382, was:
- “ Real-time is understood to mean the operation of a computing system in which programs for processing data are always ready for operation, in such a way that the processing results are available within a specified period of time. Depending on the application, the data can be distributed at random or at predetermined times. "
The hardware and software must ensure that there are no delays which could prevent compliance with this condition. The data does not have to be processed particularly quickly, it just has to be guaranteed to be fast enough for the respective application.
The Duden offers two descriptions for real time , on the one hand as a “given time that certain processes of an electronic computing system may consume in reality” and as “ time running simultaneously with reality ”. The Duden gives the following meaning for real-time operation in EDP: "The way an electronic computer system works, in which the program or data processing runs (almost) simultaneously with the corresponding processes in reality".
The term real time says something about the ability of a system to react to an event within a given time frame. The term does not say anything about the speed or processing power of a system. In colloquial language, however, this is often wrongly used instead of the more appropriate terms low- delay or low-delay .
For example, in the case of near -time data from weather satellites such as EUMETSAT , measurements that are hours old are still referred to as real-time data . Real-time is also used in applications such as passenger information systems ( dynamic passenger information ) with further processing of data in the minute range.
Depending on the type of application, this response time can vary within a wide range:
- For areas of application such as temperature control or level monitoring, response times of a few seconds are often sufficient [implemented with inexpensive microcontrollers , simple programmable logic controller (PLC)].
- Automation solutions with a programmable logic controller (PLC) or production lines based on a field bus system typically manage with response times in the millisecond range.
- Interactive applications on the computer such as games or demos require reaction times of ≤ 63 ms (≥ 15–16 images per second ) when updating the screen display in order to be perceived as a smooth process.
- The response times of computer programs to inputs by users with input devices ( keyboard , mouse, etc.) are required to be ≤ 10 ms in order to be perceived as immediate .
- Fast digital regulation , control, filtering and monitoring, online measurement data evaluation often require real-time systems that work in the microsecond range.
Real time quality
To describe a control and regulation task, however, it is not sufficient to define a real-time via the response time. In order to define the requirements for real-time systems more clearly, the reliability of meeting this response time is often defined. For this purpose, a distinction is usually made between hard real-time and soft real-time :
- hard real-time guarantees that the defined response time is never exceeded. You can rely on this property when using a hard real-time system , for example when recording the temporal course of the sensor data in a crash test .
- soft real-time , here a response time is only statistically guaranteed. Such systems typically process all incoming inputs quickly enough, but this is not guaranteed. The response time reaches, for example, an acceptable mean value or another statistical criterion. Exceeding the time requirement does not lead to errors or other technical problems.
- fixed real time is sometimes used to define a more stringent requirement than hard real time. With the fixed real time, no downward variation is allowed in the response time ( isochronous ). A practical example would be an ADC module, which ideally should work with a fixed clock rate (in reality limited by jitter of the clock).
Applications in real time are for example:
- Real-time clocks ,
- the Global Positioning System (GPS),
- the high-precision real-time positioning service and the Austrian Positioning Service ,
- Real-time passenger information systems as dynamic passenger information, for example in the Kiel region transport association or the Potsdam tram , also integrated in Google Maps ,
- the pictorial timetable for railways, inland waterway information services in inland waterway transport,
- the real-time location in the radio navigation and the flightradar24 as cyber-physical system ,
- Intelligent information system supporting observation, searching and detection for security of citizens in urban environment (INDECT), somewhat more complicated than the tried and tested test sheet for real-time recording,
- the realtime decision system (a realtime decision system in telephone marketing), as well as realtime bidding as an auction model in advertising,
- the real-time price on the stock exchange,
- Twitter and Chat ,
- the collaborative text editing in real time ,
- Intelligent Teaching And Learning with Computers ( iTALC ) and other applications in real-time collaboration ,
- Live streaming and other streaming media ,
- the Virtual Reality or less computationally intensive real-time 3D ,
- Applications in digital art , speed painting or physical modeling of sound generation in computer music and live electronics ,
- Real-time computer games such as real-time strategy games
- Applications in weather observation such as the Castor satellite ,
- in energy and environmental technology such as smart metering , the intelligent power grid or environmental information systems such as the remote sensing program Spot Vegetation ,
- a manufacturing execution system in production technology,
- Laser Speckle Extensometer for deformation measurement ,
- the Real-time MRI , 4D ultrasound , the color-coded Doppler sonography , the neurofeedback in medicine,
- the real-time PCR (English: Real Time Quantitative PCR ), an amplification method for nucleic acids,
- scientific applications such as photoemission electron microscopy , the Collider Detector at Fermilab , nuclear quadrupole resonance spectroscopy , or the gravitational wave detector when researching gravitational waves .
If the recording is done in real time with sensors and high-speed cameras, the recorded data can later be played back more slowly (in slow motion ). On the other hand, some physical models can be calculated much faster than in real time, such as star formation in a gas and dust cloud. Here the playback in fast motion is appropriate for the (scientific) interpretation.
Kaul, Susanne (ed.); Brössel, Stephan (ed.): Realtime in the film. Concepts - Effects - Contexts , Fink 2020, ISBN 978-3-8467-6251-6 .
- Software development of embedded systems: basics, modeling .
- Real time in duden.de, accessed on June 13, 2013.
- Real Time Images (satellite data processed to "real-time images" in the weather observation at EUMETSAT ), accessed on July 29, 2013.
- Boris Burger, Ondrej Paulovic, Milos Hasan: Realtime Visualization Methods in the Demoscene ( en ) In: CESCG-2002 . Technical University of Vienna . March 21, 2002. Retrieved March 21, 2011.
- Heinz Wörn, Uwe Brinkschulte: Real-time systems. Basics, functions, applications . Springer, Berlin et al. 2005, ISBN 3-540-20588-8 , pp. 321 , doi : 10.1007 / b139050 .