Parity files are file

Computer file

A computer file is a block of arbitrary information, or resource for storing information, which is available to a computer program and is usually based on some kind of durable storage. A file is durable in the sense that it remains available for programs to use after the current program has finished...

s that are created to accompany data

Data

The term data refers to qualitative or quantitative attributes of a variable or set of variables. Data are typically the results of measurements and can be the basis of graphs, images, or observations of a set of variables. Data are often viewed as the lowest level of abstraction from which...

 files, and are used to preserve data integrity

Data integrity

Data Integrity in its broadest meaning refers to the trustworthiness of system resources over their entire life cycle. In more analytic terms, it is "the representational faithfulness of information to the true state of the object that the information represents, where representational faithfulness...

 and assist in data recovery

Data recovery

Data recovery is the process of salvaging data from damaged, failed, corrupted, or inaccessible secondary storage media when it cannot be accessed normally. Often the data are being salvaged from storage media such as internal or external hard disk drives, solid-state drives , USB flash drive,...

. They are useful when data files are transmitted or stored on less-than-perfect media such as newsgroup

Newsgroup

A usenet newsgroup is a repository usually within the Usenet system, for messages posted from many users in different locations. The term may be confusing to some, because it is usually a discussion group. Newsgroups are technically distinct from, but functionally similar to, discussion forums on...

 messages, satellite transmission, or optical disk. Parity files are constructed according to algorithms of error detection and correction

Error detection and correction

In information theory and coding theory with applications in computer science and telecommunication, error detection and correction or error control are techniques that enable reliable delivery of digital data over unreliable communication channels...

.

Overview

First, one or more data files are analyzed and a group of 'parity files' are built that record the structure of the files to be protected.

Later, if any of the protected files are lost, the parity files can be used to re-create the missing files.

Even if one or more of the parity files are missing, the remainder of the set can still rebuild missing original files, if there is enough of the backup present. If too many files are missing, the parity files will not have enough base data to work with.

Parity

A parity

Parity bit

A parity bit is a bit that is added to ensure that the number of bits with the value one in a set of bits is even or odd. Parity bits are used as the simplest form of error detecting code....

 is the difference within a set of binary code. the parity of 1-0 is 1, 0-0 is 0 and 0-1 is 1, therefore lost data can be rebuilt based on the parity of a set of code.

Parity File Archiver Software

Below are examples of file archivers that create parity files. A comprehensive list of archive software is also available.

• Parchive
  Parchive
  Parchive is an open source software project that emerged in 2001 to develop a parity file format, as conceived by Tobias Rieper and Stefan Wehlus...
  
  
• SmartPAR
  SmartPAR
  SmartPAR is a freeware application for Microsoft Windows for working with Parchive format parity files. It supports the original Par1 format and uses Reed-Solomon error correction to create new recovery files. SmartPAR is able to correct errors and recover missing parts of distributed files from...
  
  
• QuickPAR
  QuickPar
  QuickPar is a computer program that creates parchives used as verification and recovery information for a file or group of files, and uses the recovery information, if available, to attempt to reconstruct the originals from the damaged files and the PAR volumes.Designed for the Microsoft Windows...
  
  

External links

• Slyck's Guide to the Newsgroups PAR and PAR2 files