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Unformatted text preview: xamples are systems that control scientific experiments, medical imaging
systems, industrial control systems and certain display systems. 3 A real time system has well defined, fixed time constraints, and if the system does
not produce output for an input within the time constraints, the system will fail. For
instance, it would not do for a robot arm to be instructed to halt after it had smashed into
the car it was building.
Real time systems come in two flavors: hard and soft. A hard real time system
guarantees that critical tasks be completed on time. This goal requires that all delays in
the system be completed on time. This goal requires that all delays in the system be
bounded, from the retrieval of stored data to the time it takes the operating system to
finish any request made of it. Secondary storage of any sort is usually limited or missing,
with data instead being stored in short-term memory or in read only memory. Most
advanced operating system features are absent too, since they tend to separate the user
from the hardware, and that separation results in uncertainty about the amount of time an
operation will take.
A less restrictive type of real time system is a soft real time system, where a critical
real-time task gets priority over other tasks, and retains that priority until it completes. As
in hard real time systems, the operating system kernel delays need to be bounded. Sof...
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This document was uploaded on 10/17/2012.
- Spring '12