Ask HN: What do you consider real-time? | Hacker News Reader

Ask HN: What do you consider real-time?

3 pointssebleon5 comments

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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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.

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

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...

Also look up RISC and RTOS

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.

Should be done in enough time to be useful.

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