Cyclic Redundancy Check

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A cyclic redundancy check (CRC) is a non-secure hash function designed to detect accidental changes to raw computer data, and commonly used in digital networks and storage devices such as hard disk drives. A CRC-enabled device calculates a short, fixed-length binary sequence, known as the CRC code or just CRC, for each block of data and sends or stores them both together. When a block is read or received the device repeats the calculation; if the new CRC does not match (or in some cases, cancel out) the one calculated earlier then the block contains a data error and the device may take corrective action such as rereading or requesting the block be sent again.

CRCs are so called as the check (data verification) code is a redundancy (it adds zero information) and cyclic (the message data circulates in the check code during calculation). The term CRC may refer to the check code or to the function that calculates it, which accepts data streams of any length as input but always outputs a fixed-length code. CRCs are popular because they are simple to implement in binary hardware, are easy to analyse mathematically, and are particularly good at detecting common errors caused by noise in transmission channels. The CRC was invented by W. Wesley Peterson, and published in his 1961 paper. The IEEE-recommended 32-bit CRC, used in Ethernet and elsewhere, appeared at a telecommunications conference in 1975.

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