Processing : Real Time Processing

For some tasks a computer must process information to meet some real world time deadline. The time deadline must be met regardless of how much work the computer has to do. Usually real time computer systems are required to process information very quickly. Most real time systems appear to process data instantly.

A computer system which must process data extremely quickly to meet a real world deadline is known as a real time system.

For example, consider a control system that is used to fly a guided missile to hit a target. Once the missile is launched the control system must guide it to its target. The missile's guidance system identifies its position by examining the contours / features of the ground it is flying over. This input data is used to ensure that the missile follows the path it has been programmed with. Using the inputs the system will decide how to move ailerons/fins to change direction and control the speed of the rocket motor.

Because a missile flies very fast the inputs must be processed very quickly to affect the outputs. If it took two seconds for the missile to change its direction to avoid an unexpected object then the missile would probably hit the object before the change of direction could take place. The data must be processed in thousandths of a second to avoid a disaster. There is a real world time limit on how long the computer system can take to process data without having terrible consequences. Therefore a missile control system has to be a real time system.

Most real time systems are control systems. Other examples include the cooling system in a nuclear reactor which prevents the reactor overheating or any system which must control a dangerous chemical reaction.

Real time systems are very fast but they do not process data instantly. Any processing will take some time. However real time systems will process data very quickly. To ensure that any input data can be processed sufficiently quickly real time systems must incorporate a lot of redundancy. This means having much more hardware than is required to process the expected amount of input data. The extra hardware is known as redundant hardware because it is not normally used. Under normal circumstances only a small fraction of the hardware is required. In extreme circumstances when there is an unusually large amount of input data to process the redundant hardware can be used. Therefore the system will not slow down and will still be capable of meeting deadlines.

Redundant hardware can also be used as backup hardware to reduce the likelihood of a computer system failing if some of its hardware fails.

Having to incorporate lots of redundant hardware makes real time systems very expensive. They are usually only used in safety critical situations.

GCSE ICT Companion 04 - (C) P Meakin 2004