Source : WordNet®

cyclic redundancy check
     n : an error correction code that is recorded in each sector of
         a magnetic disk and used to catch errors in the data

Source : Free On-Line Dictionary of Computing

cyclic redundancy check
     
         (CRC or "cyclic redundancy code") A number derived
        from, and stored or transmitted with, a block of data in order
        to detect corruption.  By recalculating the CRC and comparing
        it to the value originally transmitted, the receiver can
        detect some types of transmission errors.
     
        A CRC is more complicated than a {checksum}.  It is calculated
        using division either using {shifts} and {exclusive ORs} or
        {table lookup} ({modulo} 256 or 65536).
     
        The CRC is "redundant" in that it adds no information.  A
        single corrupted {bit} in the data will result in a one bit
        change in the calculated CRC but multiple corrupted bits may
        cancel each other out.
     
        CRCs treat blocks of input bits as coefficient-sets for
        {polynomials}.  E.g., binary 10100000 implies the polynomial:
        1*x^7 + 0*x^6 + 1*x^5 + 0*x^4 + 0*x^3 + 0*x^2 + 0*x^1 + 0*x^0.
        This is the "message polynomial".  A second polynomial, with
        constant coefficients, is called the "generator polynomial".
        This is divided into the message polynomial, giving a quotient
        and remainder.  The coefficients of the remainder form the
        bits of the final CRC.  So, an order-33 generator polynomial
        is necessary to generate a 32-bit CRC.  The exact bit-set used
        for the generator polynomial will naturally affect the CRC
        that is computed.
     
        Most CRC implementations seem to operate 8 bits at a time by
        building a table of 256 entries, representing all 256 possible
        8-bit byte combinations, and determining the effect that each
        byte will have.  CRCs are then computed using an input byte to
        select a 16- or 32-bit value from the table.  This value is
        then used to update the CRC.
     
        {Ethernet} {packets} have a 32-bit CRC.  Many disk formats
        include a CRC at some level.
     
        (1997-08-02)