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Any technique that stores ortransmits extra, derived data that can be used to detect orrepair errors, either in hardware or software. Examples areparity bits and the cyclic redundancy check.If the cost of errors is high enough, e.g. in asafety-critical system, redundancy may be used in bothhardware AND software with three separate computers programmedby three separate teams ("triple redundancy") and some systemto check that they all produce the same answer, or some kindof majority voting system.The term is not typically used for other, less beneficial,duplication of data.2. The proportion of a message's grossinformation content that can be eliminated without losingessential information.Technically, redundancy is one minus the ratio of the actualuncertainty to the maximum uncertainty. This is the fractionof the structure of the message which is determined not by thechoice of the sender, but rather by the accepted statisticalrules governing the choice of the symbols in question.[Shannon and Weaver, 1948, p. l3]