Input processing on a desktop computer can be classified as ‘soft real time’. To ensure the best user experience the computer should respond to each input within a preferred time limit – but a response falling outside of this limit will not render the computer useless. For example, key presses must be visibly registered within a certain time of the key being pressed. Registering a key press outside of this time could result in the system seeming unresponsive, but not unusable.
Multi tasking in a real time embedded system is conceptually similar to multi tasking in a desktop system to the point that it describes multiple threads of execution using a single processor. However the objectives of real time embedded systems are likely to be quite different to that of desktops – especially when the embedded system is expected to provide ‘hard real time’ behavior.
Hard real time functions must complete within a given time limit – failure to do so will result in absolute failure of the system. The airbag triggering mechanism in a car is an example of a hard real time function. The airbag must deploy within a given time limit of an impact. A response falling outside of this time limit can result in the driver sustaining injuries that would otherwise have been avoided
