Michael Segel 2012-10-02, 12:04
There is an important difference between real time and real fast
Real time means that system response must meet a fixed schedule.
Real fast just means sooner is better.
Real time systems always have hard schedules. The schedule could be in microseconds to control a laser for making masks for semiconductor manufacturing, milliseconds to control the ignition in your car or flight controls on an F-22 or seconds for even slower moving processes. In real time system missing the schedule can mean that very bad things happen: planes fall from the sky, your laser printer fries it's imaging drum, factories explode etc.
Most transaction processing is happy with real fast
The folks doing high velocity trading are pretty close to real time but they probably will be happy with real fast.
If real fast systems miss a schedule then someone loses money.
The reason that RTOS type operating systems are popular for real time applications is that they don't allow operations to spend indeterminate amounts of time in uninterruptable states. Java will never qualify as a real time system because it has garbage collection and garbage collection can lock up a system for an indefinite amount of time while it goes through marking and counting.