But, What is real time?
Real Time in Software.
So, it's important to realize which use case your real time system is handling -- whether you're time-bound to ensure you avoid catastrophe or you're chasing time's tail to maximize profit. Once you determine your constraint, it's easier to design systems, select the right architecture & tools to achieve that.
For interesting evolution of the term real time, see Phillip Laplante's article on It Isn’t Your Father’s Realtime Anymore at: http://queue.acm.org/detail.cfm?id=1117409