Talk:Real-time computing

message: The distinction between hard and soft is incorrectly stated. An RTOS is hard when the consequences of not meeting time constraints are severely unacceptable -- typically, medical and other life-threatening situations. Most commercial RTOSs form soft systems, not hard. (I have the time neither to correct the mistakes nor to provide the requisite references.) P00r 04:03, 1 May 2007 (UTC)
thread_title:  Hard vs. Soft 

message: I'm not going to edit the entry, but I want to make an observation.  There are real-time systems in which failure can occur if an operation starts too soon.  I deal with such systems frequently.  One example is a half-duplex serial connection where one side must delay sending data until the other side has had time to tri-state the shared communication line.  Another is a system where one process reads data that must arrive from another from within recurring assigned time windows.  An example might be a simple star network, where a central processor takes data from a number of external processors, each of which has well-defined time windows assigned to it.
Jive Dadson 21:10, 20 June 2006 (UTC)
thread_title:  Too soon can be as bad as too late 

message: What's up with real-time? Its talk page links here, and most of the useful information in it is better explained here or in the RTOS entry. Some of the information on it (Gartner forcasts a fast increase...) is out-of-place, or at the very least needs to be properly cited. And the whole entry needs better organization. I think either we should try to merge "Real-time computing" into a section of "Real-time", or delete the latter. piman 03:09, 2005 Feb 27 (UTC)
:My vote is to merge Real-Time computing" to Real-time" Symphonic
::I'm much more active on the Dutch Wikipedia than I am here, but I can't help myself today: The real-time-article is also used to explain some other real-time activities, like real-time chat on WP:IRC. So you guys might want to take this into account in discussing wheter these two articles should be merged. MigGroningen 20:15, 19 February 2006 (UTC)
replies: text: I agree, merge. This article primarily relates to computing. It should be merged, and "Real-time" should either be what's Real-time (media) now, or some overall explanation of the concept (which I don't think has been written here yet), or just a disambiguation page.   --Howdybob 13:53, 16 May 2006 (UTC)
replies: text:  I feel the disambiguation is necessary, as there exist many different concepts of real-time. Why should it be incorrect?? Fuffzsch 13:52, 7 November 2006 (UTC)

text:  I agree with using a disambiguation. To find out what the term means, you should use a dictionary, not an encyclopedia. 108.6.2.66 (talk) 18:46, 13 May 2010 (UTC)
thread_title: Proposed merger or other reorganizations

message: I would like to ask how does the real time operating system achieve the task in real time.How does it make sure that the given task is finished in the given amount of time.
:Different RTOSs may do different things when a task does not complete in its alloted time (e.g., kill it and log an error, abort it this time and raise its priority for the next time, kill less critical tasks). In some cases they may do different things for different tasks (e.g., a flight critical task may be allowed to complete even if it runs over its alloted time, but non-flight critical tasks get killed to give the flight critical ones more time in the future). These are usually designer/programmer decisions and the RTOS must be properly configured to meet the system requirements.
:But sometimes the RTOS doesn't even get a say in the matter, if the task doesn't complete in the alloted time it will never complete due to external "real world" events. The best example I ever heard of this was someone's description of a real time data collection computer they were working on that came up in a conference on design methodologies: "I don't think you understand what I mean when I say real time system. The system I am working on is attached at one end of a one meter long steel rod, at the other end of which is a nuclear bomb. It begins collecting data and transmitting it over a high speed link to another computer just before detonation. This system MUST complete all tasks before the radiation from the explosion destroys the processor. That is what I mean by real time system." That is an example of a true hard real time system. -- RTC 00:20 Apr 24, 2003 (UTC)
:: I recognise this anecdote from Tom Demarco's Foreword to Hatley D and Pirbhia I, Strategies for Real-Time System Specification, Dorset House Publishing, New York 1988 . With Tom's usual talent for the snappy, he uses the example to differentiate real-time from just 'quick as a bunny'  Atconsul (talk) 08:39, 10 May 2013 (UTC)
thread_title: Other subjects

message: Can anyone explain what is a firm real-time system and how is it different from hard and soft real-time systems? One definition I found was that systems which are soft real-time but in which there is no benefit from late delivery of service. Confused me further...
:There is a lot of confusion about what constitutes a soft real-time system even among researchers. There are, however, a few classical versions. One of these is the notion of firm real-time (and the only one of these variants that I know even has a name). With firm deadlines, deadlines may occasionally be missed, but there is no use of continuing the work after the deadline. Typically there are borders on how many misses are acceptable (i.e. max 3% deadline miss ratio). This is in perfect correspondence with the definition you found. Basically, after the deadline, the computation is useless, so you might as well skip to the "next" computation as soon as the system realises that the deadline will be missed (in many system this is at the deadline, but potentially it could be earlier).
:For comparison, another notion of soft real time systems is the one where some jobs may occasionally be slightly late, but still have to be performed. Further, there are several other interpretations floating around, and as said, quite much confusion. If you have access to a university library, this paper might be an interesting read to clarify some of the confusion. TERdON (talk) 16:00, 15 October 2008 (UTC)
replies: text: The last paragraph is indeed very questionable. Wikipedia is the wrong place for wild guesses about the future and it sounds like pure marketing bullshit blather. I bet whoever added that is affiliated with Gartner or just loves bullshit bingo. --82.141.57.73 01:00, 8 July 2006 (UTC)
thread_title: Firm Real-time System

message: I cannot follow the idea to merge real-time with real-time computing, as real-time is a broader subject than real-time computing. Although, the matter of real-time is not only a matter of computation. So, neither of these themes are a subset of the other.
There are real-time networks, real-time secure networks. Of course, they do have some software, but that is only part of it.
SAE1962 13:24, 29 June 2006 (UTC)
thread_title:  Real-time not a subset of computing! 

message: "It would not be possible to offer modern commercial air travel if these computations could not reliably be performed in real time."  This is simply untrue, since "modern commercial air travel" existed long before the development of the microchip; indeed, before even ENIAC.  Depends what's meant by "modern commercial air travel"...as a reader, I think "modern commercial air travel" certainly existed when people were boarding DC-3s in the 1930s.  Perhaps the original author can clarify.
There has been tremendous misuse of the expression "real time"
Most people confuse online rapid response with real time.
"Real time" means synchronized with the clock.
Notice a NASA missile launch.  "T-10 and counting".
The missile does not ignite when ready but is poised to ignite
at just the right second and every operation is the synchronized 
with the clock.  "Shut off" occurs at just the right time.
Collecting telemetry live from an aircraft is not real time.
It is rapid and with minimum delay but it is not synchronized
with the clock.
68.50.127.210 19:02, 6 July 2007 (UTC)
thread_title:  Modern Air Travel 

message: Firm real-time system is a system in which a completion of an operation after its deadline is considered useless, but the system can withstand a few missed operations.
Ehudhal 03:33, 12 September 2007 (UTC)
thread_title:  Firm Real-time System 

message: real time has been used/defined wrongly in this article. real time means the ability of a system to be modified whille running by changing its input....i will try and get some references to journals.  Prince Waters (talk page) 20:45, 7 December 2009 (UTC)
thread_title: real time used wrongly

message: How does the definition of "real time" relate to getting interrupted by the OS?
It seems like when I hear people talking about RT programming they talk about assurances that nothing else is going to interfere with a certain task.
Is this what RT programming is all about or a side aspect of RT programming?  —Preceding unsigned comment added by 214.4.3.75 (talk) 01:54, 3 April 2010 (UTC)
thread_title:  scheduling / interrupting tasks 

message: Some of the External Links are presently dead or pointing to confusing redirects:
International Symposium on Object-oriented Real-time distributed Computing (dead link)
Real-time, Embedded, and Specialized Systems Platform Task Force (confusing redirect to http://www.omg.org/homepages/index.htm which doesn't mention realtime) --Donkeydonkeydonkeydonkey (talk) 21:22, 23 July 2010 (UTC)
replies: text: Thank you for finding these; if you want, you can be bold and update Wikipedia articles yourself. I replaced the first link with <http://www.informatik.uni-trier.de/~ley/db/conf/isorc/index.html>, which appears to be a listing of past conferences; I am not positive that it is from the organizers and will be updated for 2010, so there may be a better link out there. For the second, that Platform Task Force appears no longer to exist (see <http://www.omg.org/homepages/index.htm> and scroll to Platform Technology Committee), so I removed it. There does appear to be a relevant conference at <http://www.omg.org/news/meetings/SMCS/rt/Program.htm>, if anyone prefers to replace than remove. - 2/0 (cont.) 00:06, 24 July 2010 (UTC)
thread_title:  Dead links 

message: This is uncited and, in some cases, dubious.  It's also unclear what real value such a list adds to the article.  I'm leaving it here in talk for now.  
* Sanjoy Baruah
* Alan Burns
* Giorgio Buttazzo
* Costas Courcoubetis
* David Dill
* Nicolas Halbwachs
* Hermann Kopetz
* Arthur Pollen
* Bruce Douglass
* John Stankovic
* Lui Sha
Fell Gleamingtalk 02:58, 14 September 2010 (UTC)
thread_title:  Key People 

message: After examining the Wikipedia article Real-Time Computing and Talk - the situation remains confused and uninformed. Rather than getting wrapped around the flag pole on definitions, it would be preferable if Wikipedia were to adhere to the modern accepted canon (developed after close to forty years of academic and industrial research, defense and commercial real-time software/firmware development projects - some embedded, some standalone) that now reflect best practices. All interested parties should read Real-Time Scheduling: A Historical Perspective[1], Dr. Lui Sha,[2] Editor. In contemporary use Real-Time Computing[3] is routinely considered a canonically distinct element of Real-Time Systems[4], just as Real-Time Scheduling is treated pedagogically as a supporting element of Real-Time Computing. Also, refer to Real-Time Talk.
:[1] Sha04-RTSJ.pdf (available free on Google Scholar)
:[2] Donald B. Gillies Professor of Computer Science, University of Illinois
:[3] Real-Time Systems, J.W.S. Liu, April 2000, Prentice-Hall Publ., Chapters 1,2
:[4] Ibid.
Ken Fowler, PhD.
Kenfowler1945 (talk) 22:08, 4 March 2012 (UTC)
thread_title:  MOVING FROM BABEL TO SCIENCE -- REAL-TIME COMPUTING  

message: I still can't work out what usefully distinguishes a RTOS from a non-RT OS.
"..."deterministic" timing means that operating system services consume only known and expected amounts of time."
Almost all the system calls in my 6502-based BBC Micro were listed with the times the calls took. Does that make it a RTOS?
Deterministic timing seems to mean that a RTOS must never interact with a user ever as it is unknown how long the user is going to take. A RTOS must never interact with any IO devices ever. It is impossible to know how long, eg, a disk drive or printer or actionator solenoid is going to take to respond. A RTOS must never run on a system with interupts running, as an interupt could occur during a call and add extra time to the call. All of this seems to essentially say that a RTOS is an unattaintable idealistic system with no useful purpose.
Jgharston (talk) 23:06, 25 July 2012 (UTC)
thread_title:  Still puzzled 

message: I'm considering what I believe to be merely a semantic correction, but as I'm not an expert in real-time programming I want to be sure that I don't alter the intended meaning of the sentence.  The sentence in question is from the opening section, and currently reads, "In the domain of simulations, the term means that the simulation's clock runs as fast as a real clock."  I'm pretty sure that what was intended was, "In the domain of simulations, the term means that the simulation's clock runs at the same speed as a real clock."  The phrase runs as fast as can reasonably be construed to still be true if the simulation clock runs faster than a real clock.  In other words, at least as fast can reasonably be inferred from how the sentence is currently written.
Would my proposed change more accurately convey the intent of the sentence?Tedd (talk) 22:14, 23 October 2013 (UTC)
thread_title:  "...as fast as a real clock." 

message: According to a learned colleague of mine, it is impossible to discuss Time-utility function without Real-time computing.   Since Time-utility function has been tagged for notability and lack of references for four years, a merger would also be appropriate. Bearian (talk) 21:21, 4 February 2014 (UTC)
replies: text: Yes, please merge whatever is appropriate from Time-utility function to here and change the other article to redirect to here. Thank you. 71.169.179.188 (talk) 05:49, 5 February 2014 (UTC)

text: Oppose: Time-utility function isn't a term specific to real-time computing only; please have a look at Adaptive Time-utility Function Scheme for Downlink Packet Scheduling in IEEE 802.16e/WiMAX Networks, for example. — Dsimic (talk | contribs) 05:57, 5 February 2014 (UTC)
replies: text:  My goodness, that paper you refer to does the opposite of supporting your case that time-utility function is unrelated to (or whatever is meant by not "specific to") real-time computing.  It appears that it is intimately related.  I am a DSP engineer, both real-time and non-real-time processing, and I have some experience in other real-time embedded systems and I am not familiar with specifically what "time-utility function" is as a semantic.  But I imagine as I read more about it, I am going to find out that even if there is some application of the concept of "time-utility function" to non-real-time targets, that the concept really is primarily about real-time processing and the efficacious scheduling of tasks. 71.169.179.188 (talk) 15:59, 5 February 2014 (UTC)
replies: text:  Sorry, I wasn't clear enough, please allow me to explain.  When people talk about real-time computing, they usually think of real-time operating systems (RTOSs), and what I tried to say was that the time-utility function isn't bounded to be used in RTOSs only.  That's the reason why I'm suggesting that it should be kept as a separate article, so it's clear that it—as a scheduling function, basically—can be used for many purposes.  Hope it now makes more sense. — Dsimic (talk | contribs) 16:21, 5 February 2014 (UTC)
replies: text:  What are the some of the other "many purposes"?  It is true that real-time computing is not the same as high-performance computing, but it is related (if the CPU speed is not sufficient, the real-time performance suffers).  Similarly it is true that real-time computing, as a topic is not the same as real-time operating system, but they are, of course, related.  It appears that this time-utility function is directly related to efficacy of certain processes that affect deadlines.  If that is the case, and if time-utility function is small enough and narrow enough to not deserve it's own page (because it looks like a stub), then it should be folded in with the broader topic that contains it.  71.169.179.188 (talk) 17:49, 5 February 2014 (UTC)
replies: text:  The above linked paper illustates use of the time-utility function for network packets scheduling in a real-time manner, and not as part of an RTOS.  As another example, this paper describes its use in heterogeneous systems (computer clusters, which are hardly of a real-time nature).  Having that in mind, the Time-utility function article could be easily expanded to at least five times its current size.  Hence, my opinion is that it shouldn't be merged as it can be expanded of course, that's just my opinion, and we don't have to agree there. :) — Dsimic (talk | contribs) 18:11, 5 February 2014 (UTC)
replies: text:  I support the merge. Please appreciate that the proposed target is Real-time computing not Real-time operating system. The former should encompass wider aspects of computing including networking. ~KvnG 15:01, 17 February 2014 (UTC)
thread_title:  Merge from [[Time-utility function]] 

message: Although I could not get Google Books to confirm the citation from Martin, I have found this definition of "real-time" of Martin's cited by other authors.
It's a good definition and I think it should stay.  I have also confirmed my edit removing the "d" 71.169.179.28 (talk) 16:23, 27 April 2014 (UTC)
replies: text: Sorry, I think you're right about "and".  I  have  the hardcopy  book, but wanted  to include some sort  of link to a source  on  Google or Amazon. Peter Flass (talk) 16:38, 27 April 2014 (UTC)
thread_title:  Martin citation 

message: A single article used to distinguish between three distinctly different and accepted meanings of real-time. Some months ago, they were then separated into two articles in a incomplete way and the mixed meanings remain in each new article, and the third meaning was dropped altogether. The differences between the two remaining meanings remain mixed, and aren't distinguished, making for a confusing read. Now there is a proposal to merge these articles (re-merge), without realizing that they were once a single, well segmented article. Many of the comments on this page refer to the ambiguity and confusion that has arrisen from people accustomed to one particular distinct definition.  — Preceding unsigned comment added by 130.216.49.8 (talk) 19:46, 25 June 2014 (UTC)
replies: text: What is the second article you're referring to? ~KvnG 13:25, 3 July 2014 (UTC)
thread_title:  Merge vs No merge 

message: The External links section needs some serious trimming to comply with WP:EL. As a start, I have marked the dead links there. I've checked to see if any of the items referenced in the section has a corresponding Wikipedia article. I've found List of computer science conferences, Kang_G._Shin#Real-Time_Computing_Laboratory_.28RTCL.29, Sant%27Anna_School_of_Advanced_Studies#Laboratories_and_research_centers, Simula Research Laboratory. Nothing really worthy of a See also link. We might consider moving this to DMOZ at . We might just want to delete it all. ~Kvng (talk) 16:35, 6 July 2015 (UTC)
replies: text: Hello!  Got the section  in theory, having all those external links might have been great, but in practice, 99.9% of the readers had absolutely no use for them.  Hope you agree. — Dsimic (talk | contribs) 19:41, 6 July 2015 (UTC)
thread_title:  External links 

message: Plan9 has a real time scheduling option, this seems like a good real-world example, but I'm not sure how to fit this in. Binarycat64 (talk) 23:58, 4 November 2021 (UTC)
thread_title:  Real world example (plan9) 

message: There's currently a link to DSOS, which seems oddly specific as an example of an RTOS. Maybe replace this with a broader link to the general RTOS article? Liftyee (talk) 14:11, 12 March 2022 (UTC)
thread_title:  Insert link to "Real time operating system" at the end?