Parchive (a portmanteau of parity archive, and formally known as Parity Volume Set Specification) is an erasure code system that produces par files for checksum verification of data integrity, with the capability to perform data recovery operations that can repair or regenerate corrupted or missing data. Parchive was originally written to solve the problem of reliable file sharing on Usenet, but it is now commonly used for protecting any kind of data from data corruption, bit rot, and accidental or malicious damage. Despite the name, Parchive uses more advanced techniques that do not utilize simplistic parity methods of error detection and correction.
The original SourceForge Parchive project has been inactive since November 9, 2010. As of 2014, Par1 is obsolete, Par2 is mature for widespread use, and Par3 is an experimental version being developed by MultiPar author Yutaka Sawada.
Parchive was intended to increase the reliability of transferring files via Usenet newsgroups. Usenet was originally designed for informal conversations, and the underlying protocol, NNTP was not designed to transmit arbitrary binary data. Another limitation, which was acceptable for conversations but not for files, was that messages were normally fairly short in length and limited to 7-bit ASCII text.
In the context of spaceflight, a satellite is an artificial object which has been intentionally placed into orbit. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as Earth's Moon.
The world's first artificial satellite, the Sputnik 1, was launched by the Soviet Union in 1957. Since then, thousands of satellites have been launched into orbit around the Earth. Some satellites, notably space stations, have been launched in parts and assembled in orbit. Artificial satellites originate from more than 40 countries and have used the satellite launching capabilities of ten nations. About a thousand satellites are currently operational, whereas thousands of unused satellites and satellite fragments orbit the Earth as space debris. A few space probes have been placed into orbit around other bodies and become artificial satellites to the Moon, Mercury, Venus, Mars, Jupiter, Saturn, Vesta, Eros, Ceres, and the Sun.
A satellite is a subviral agent composed of nucleic acid that depends on the co-infection of a host cell with a helper or master virus for its replication. When a satellite encodes the coat protein in which its nucleic acid is encapsidated it is referred to as a satellite virus. A satellite virus of mamavirus that inhibits the replication of its host has been termed a virophage. However, the usage of this term remains controversial due to the lack of fundamental differences between virophages and classical satellite viruses.
The genomes of satellites range upward from 359 nucleotides in length for Satellite Tobacco Ringspot Virus RNA (STobRV).
Satellite viral particles should not be confused with satellite DNA.