Real-Time Operating Systems are systems in which certain processes or operations have
guaranteed minimum and/or maximum response times - that is, the system ensures that it will complete operation
x after time
t but before time
t', whatever
t and
t' are, without fail, even at the expense of other lower priority operations. Generally, it only applies to time-dependent embedded systems. 'Soft' real-time systems (e.g., laser-printer microcontrollers) promise
best-effort reliability; 'hard' real-time systems (e.g., 'fly-by-wire' avionics in an aircraft) need to have
zero-failure-tolerance reliability.
Note that this is
not about speed, per se; the fastest system possible would not be RT, unless it could
guarantee that the operation will be finished within the time constraints. Furthermore, a response time less than
t may be just as bad as one greater than
t', if not worse.
If you aren't looking at an embedded systems problem, you probably don't need to be working with RT.
You might want to check out these threads, where the topic has been discussed in detail.
What is a Real-Time OS?
Real-time Operating system
Real-Time Kernels
Real-Time Scheduling