Real-time computing happens when a system is able to guarantee its latency time, regardless of the system load. Obviously, low latency times are mandatory, but it is the ability to guarantee the same latency time as load increases that makes a fast system actually a real-time system. A more detailed definition is available here: http://en.wikipedia.org/wiki/Real-time_computing.
A canonical example is the ABS (anti-lock braking system) logic ubiquitously implemented in any automobile. Such logic must give results within a specific deadline (in a span of milliseconds), otherwise the system will go into a failed state.
Sometimes real-time systems may run at an acceptable service level, although with soft constraint specifications such as adding some tolerance to the deadline requirement. With such a near real-time requirement, we can code in .NET for Microsoft Windows as easily as we usually do for any other application type.
Bear in mind that within Microsoft Windows we...