
Ask HN: What do you consider real-time? - sebleon
Forget the marketing-speak, curious to see what formal definitions are used. Are these typically system response latency cutoffs that vary by industry? ie. 1 second would not be real-time for algo trading, but might be for tweet aggregation for brands
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jsegura
If we speak about human interactions, I think that it should be less than
250ms.

In 1968 Robert Miller published his classic paper _Response time in man-
computer conversational transactions_ in which he described three different
orders of magnitude of computer mainframe responsiveness:

\- A response time of 100ms is perceived as instantaneous.

\- Response times of 1 second or less are fast enough for users to feel they
are interacting freely with the information.

\- Response times greater than 10 seconds completely lose the user’s
attention.

But I totally agree with you, it totally depends on what is the purpose of
your system.

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sebleon
Good point, I wish this was better understood by the engineers at Gmail

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devnonymous
Historically speaking real time was not actually about absolute timing but the
guarantee offered about a task's completion within a time slice.

More info here: [https://en.m.wikipedia.org/wiki/Real-
time_computing#Criteria...](https://en.m.wikipedia.org/wiki/Real-
time_computing#Criteria_for_real-time_computing)

Also look up RISC and RTOS

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brudgers
My relatively non-formally informed opinion is that one property that seems to
correlate with real time is:

    
    
      R ≤ S
    

Where R is the maximum time it takes to return a useful result and S is the
maximum sample rate. Anything else suggests that results queue up and hence
the time to return a result varies.

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ankurdhama
Should be done in enough time to be useful.

