From my earliest days in measurement, the term "real-time" has been special. Its meaning has evolved over these years as a figure of merit without any actual figures being presented. But the use has continually increased as a way of denoting the presence of data as it occurs.
What exactly is real-time, anyway? Many may say it is "in the eye of the beholder." The other caveat is that it be available "fast" (whatever that means).
How can a term be so widely used, yet be so vague? Its usefulness is its greatest asset. Without getting hung up on specifications, real-time is a way of describing a process without latency. That's what's so special about real-time. Folks can talk to folks, have complete understanding of what they are looking at, and be happy that they have common understanding.
Face-to-face conversations always take place in real-time.
With data acquisition, we have to go beyond this overall term to actually specify the time at which data will be presented. I'm not talking just measured data, but collected, processed, and presented data in final, useful form. Again, this has evolved as measurement speeds have increased from microseconds to nanoseconds. On-the-fly processing provides "instant" results for the user. The ability to measure in real-time can produce processed results that keep up with the actual input data stream.
These types of fast systems have always cost more than conventional data-collection systems that run, say, Windows. Many of these systems have DSP (digital signal processing) capability where the mean processing time is no greater than the sampling period. But, the cost of these systems prevented their widespread use.
Open-source hardware such as the BeagleBone Black is making its way into measurement systems.
My prediction is that cost will decrease and usage of such fast real-time systems will increase. The reason for that will be the inclusion of ARM processing on almost any measurement system of the future. Platforms such as BeagleBone Black and its derivatives are now being designed into standard measurement systems. These new modules and systems will increase real-time data for industrial and scientific applications at a reasonable cost.