 Open Source Real-Time Operating Systems
Rafeeq Ur Rehman
A real-time operating system performs its functions and responds
to external events, such as interrupts, within a specified period
of time. The term "real-time" means that the system responds
to events as they occur. Real-time systems play a very important
role in daily life. Common applications of these systems include
air traffic control systems, telecommunication equipment, routing
and switching products, and medical imaging systems. In manufacturing
industry, real-time systems control robots used in various automatic
processes.
In real-time system terminology, a deadline is a time interval
during which a real-time system must respond to an event. Deadline
requirements for different real-time systems may vary. In some circumstances,
results produced after deadline are not only considered late but
are also considered wrong. In other systems, these may be tolerated.
Depending upon the strictness of their timing requirements for meeting
deadlines, systems are categorized as hard or soft real-time systems.
A real-time task is hard if that inability to meet a deadline results
in catastrophe. A real-time task is soft when meeting the deadline
is desirable, but missing a deadline does not result in incorrect
system behavior or catastrophe.
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