Real-time computing is typically thought of control systems for mission critical computers - airplanes that cant' fall out of the sky, nuclear plants, oil refineries, pharmaceutical manufacturing.

(Electronics & Computer Science / Computer Science) denoting or relating to a data-processing system in which a computer receives constantly changing data, such as information relating to air-traffic control, travel booking systems, etc., and processes it sufficiently rapidly to be able to control the source of the data

The desktop could do real-time things, but it wasn't designed to be a real-time computer. Sometimes there are long delays where you get hour glass or spinning wheel. A real-time system was used because failure of the system to respond in an accepted amount of time was not acceptable.

With the rapid growth of Mobile and people's expectation of a good UI experience. What app succeeds that makes users wait? or even worse wait longer at random times. In the users eye, the app is broken. That app will quickly lose users and fail. Guess what users expect real-time response.

I found this table of user response time. The 0.1 second is a general rule of thumb. But, what mobile users would wait 10 seconds?

able 7-1 Maximum acceptable response times for typical events

UI Event Maximum Acceptable Response Time

Mouse click, pointer movement, window movement or resizing, keypress, button press, drawing gesture, other UI input event involving hand-eye co-ordination 0.1 second

Displaying progress indicators, completing ordinary user commands (e.g. closing a window), completing background tasks (e.g. reformatting a table) 1.0 second

Displaying a graph or anything else a typical user would expect to take time (e.g. displaying a new list of all a company's financial transactions for an accounting period) 10.0 seconds

Accepting and processing all user input to any task 10.0 seconds

And, does even 0.10 second feel too long. If you are playing a game a 0.10 delay could totally change the game experience.

Guess what users expectations are that systems perform like real time systems.