Real-time computing

The last chapter provided a brief introduction to some of the requirements of real-time computing in terms of a system’s responsiveness to changes in its inputs. These requirements are specified in the form of timing deadlines that limit how long the system can take to produce an output in response to a change in its input. This section looks at these timing specifications in more detail and presents some of the features real-time computing systems implement to ensure timing requirements are met.

Real-time computing systems can be categorized as providing soft or hard guarantees of responsiveness. A soft real-time system is considered to perform acceptably if it meets its desired response time most, but not necessarily all, of the time. An example of a soft real-time application is the clock display on a cell phone. When opening the clock display, some implementations momentarily present the time that was shown the last time the clock display was used...