Redundancy

Redundancy is the inclusion of information or resources beyond what is strictly necessary to represent a message or perform a task. It can improve reliability, enable error correction, or create unnecessary duplication.

Error-correcting code: A code that adds structured extra symbols so messages can be detected or recovered despite errors. These codes use deliberate redundancy to reconstruct data corrupted in transmission or storage.
Redundant array of independent disks: A storage arrangement that combines multiple disks for performance, capacity, or fault tolerance. Some RAID levels store duplicate data so a disk failure need not destroy it.
Data compression: The encoding of data in a form that uses fewer bits than an original representation. Compression removes predictable structure that redundancy makes available.
Shannon's source coding theorem: A theorem giving the limit on the average code length for lossless representation of a source. It formalizes how predictable information can be encoded using fewer symbols.
Checksum: A computed value used to detect changes or errors in data. A checksum adds a compact check value that reveals some transmission or storage errors.
Replication (computing): The maintenance of multiple copies of data or services across computing systems. Replicas provide spare copies when a server or storage location becomes unavailable.
Lossless compression: A compression method that reconstructs the original data exactly from its encoded form. It exploits redundancy without permanently discarding information.
Shannon–Hartley theorem: A theorem specifying the maximum reliable data rate of a band-limited noisy communication channel. It quantifies how channel noise constrains reliable communication despite coding redundancy.
Parity bit: An extra bit set to make a group of bits have even or odd parity. It is a simple, concrete form of added redundancy for detecting bit errors.
Network redundancy: The provision of alternate network links or equipment to maintain connectivity after failures. Extra routes and devices keep communication possible when a component fails.

Linked from 5 pages