Editing Real-time computing (section)

{{short description|Study of hardware and software systems that have a "real-time constraint"}}
{{distinguish|text=[[Real-time communication]] or [[Real-time clock]], closely related technologies that are also often abbreviated to RTC}}
{{Refimprove|date=April 2014}}

'''Real-time computing''' ('''RTC''') is the [[computer science]] term for [[Computer hardware|hardware]] and [[software]] systems subject to a "real-time constraint", for example from [[Event (synchronization primitive)|event]] to [[Event (computing)|system response]].<ref>{{Cite web |title=FreeRTOS – Open Source RTOS Kernel for small embedded systems – What is FreeRTOS FAQ? |url=https://www.freertos.org/FAQWhat.html#WhyUseRTOS |access-date=2021-03-08 |website=FreeRTOS |language=en-US}}</ref> Real-time programs must guarantee response within specified time constraints, often referred to as "deadlines".<ref name="Ben-Ari-pg164">[[Mordechai Ben-Ari|Ben-Ari, Mordechai]]; "Principles of Concurrent and Distributed Programming", ch. 16, Prentice Hall, 1990, {{ISBN|0-13-711821-X}}, p. 164</ref>

The term "real-time" is also used in [[Computer simulation|simulation]] to mean that the simulation's clock runs at the same speed as a real clock.

Real-time responses are often understood to be in the order of milliseconds, and sometimes microseconds. A system not specified as operating in real time cannot usually ''guarantee'' a response within any timeframe, although ''typical'' or ''expected'' response times may be given. Real-time processing ''fails'' if not completed within a specified deadline relative to an event; deadlines must always be met, regardless of [[Load (computing)|system load]].

A real-time system has been described as one which "controls an environment by receiving data, processing them, and returning the results sufficiently quickly to affect the environment at that time".<ref>{{cite book |last=Martin |first=James |url=https://archive.org/details/programmingrealt0000mart |title=Programming Real-time Computer Systems |date=1965 |publisher=Prentice-Hall Incorporated |isbn=978-0-13-730507-0 |location=Englewood Cliffs, New Jersey |page=[https://archive.org/details/programmingrealt0000mart/page/4 4] |language=en-us |url-access=registration}}</ref> The term "real-time" is used in [[Industrial control system|process control]] and [[enterprise system]]s to mean "without significant delay".

Real-time software may use one or more of the following: [[synchronous programming language]]s, [[real-time operating system]]s (RTOSes), and real-time networks. Each of these provide essential frameworks on which to build a real-time software application.

Systems used for many [[Safety-critical system|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.<ref>{{cite book
 | url = https://books.google.com/books?id=3714jIryozYC&pg=PA356
 | title = Computer-Based Industrial Control 
 | date = May 2010 | access-date = 2015-01-17
 | first=Krishna |last=Kant | publisher = PHI Learning
 | page = 356
| isbn = 9788120339880 
 }}</ref>