<algorithm> (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)

A cyclic redundancy check (CRC) is an error-detecting code commonly used in digital networks and storage devices to detect accidental changes to digital data. Blocks of data entering these systems get a short check value attached, based on the remainder of a polynomial division of their contents.

<storage, communications> (VRC) An error checking method performed on one 8-bit ASCII character, where the 8th bit is used as the parity bit. The resulting parity bit is constructed by XORing the word. The result is a "1" if there is an odd number of 1s, and a "0" if there is an even number of 1s in the word. This method is unreliable because if an odd number of bits are distorted, the check will not detect the error. The Longitudinal Redundancy Check is an improvement. (2001-04-28)

In telecommunications, a transverse redundancy check (TRC) or vertical redundancy check is a redundancy check for synchronized parallel bits applied once per bit time, across the bit streams. This requires additional parallel channels for the check bit or bits.

cyclic redundancy check

In telecommunication, a longitudinal redundancy check (LRC), or horizontal redundancy check, is a form of redundancy check that is applied independently to each of a parallel group of bit streams. The data must be divided into transmission blocks, to which the additional check data is added.

<storage, communications> (LRC, Block Redundancy Check) An error checking method that generates a longitudinal parity byte from a specified string or block of bytes on a longitudinal track. The longitudinal parity byte is created by placing individual bytes of a string in a two-dimensional array and performing a Vertical Redundancy Check vertically and horizontally on the array, creating an extra byte. This is an improvement over the VRC because it will catch two errors in the individual characters of the string, beyond the odd errors. (2004-01-26)

Redundancy in United Kingdom law concerns the rights of employees if they are dismissed for economic reasons in UK labour law.

n. a check issued by a bank on its own account for the amount paid to the bank by the purchaser with a named payee, and stating the name of the party purchasing the check (the remitter). The check is received as cash since it is guaranteed by the bank and does not depend on the account of a private individual or business. Cashiers' checks are commonly used when payment must be credited immediately upon receipt for business, real estate transfers, tax payments and the like.