A redundancy check is a number that is calculated from a file or a segment thereof and then appended to that file or segment for the purpose of comparing with a recalculation by another computer or at a later date in order to detect and correct errors that might occur during any phase of the storage or transmission of the file or segment.
The most simple types of redundancy checks are checksums. For example, the number of bits in a file could be counted and this number stored in the file along with its data. In a slightly more advanced type of checksum, the number of binary ones in the file would be counted and that number would stored in the file.
Redundancy checks are used extensively in computers and communications, and a number of algorithms have been developed for them. In addition to various types of checksums, they include cyclic redundancy checks, horizontal redundancy checks, vertical redundancy checks and cryptographic message digests.
In general, the simplest types of redundancy checks detect fewer errors than the more sophisticated types. However, they have the advantage of lower overhead (i.e., processor time and bandwidth). The overhead penalty of the more sophisticated types has become relatively unimportant in recent years as a result of the rapid growth in processor speeds and bandwidth.
Created November 3, 2005.