Par and Par2 files are used to repair damaged files based on their binary pattern. The name Par comes from Parity. They are also able to rebuild missing files. [PAR]ity files are used to reconstruct files that are missing from the archive. For example, if you have downloaded an archive that was split into 47 files but one of them is missing, you could simply download a PAR file for that archive. Once you have the PAR file, you can use a PAR program to reconstruct the missing file. PAR files are sometimes spotted in binary-oriented Usenet newsgroups, where their reconstructability helps compensate for the unreliablity of Usenet news propegation.

PAR files are simple to spot. They use the following extension system: .PAR, .P01, .P02, .P03, etc.

The .PAR file is an index file for the set and does not count towards reconstructing any files (it is usually less than 1K). The .PAR file is the one you open in the PAR program, although if it is missing also, it is not critical and the reconstruction will still work by opening any of the actual PAR files.

PAR2 files generally use this naming/extension system: filename.vol000+01.PAR2, filename.vol001+02.PAR2, filename.vol003+04.PAR2, filename.vol007+06.PAR2, etc

The +01, +02, etc in the filename indicates how many 'blocks' it will be able to repair.

In both PAR and PAR2 any one of the repair files can be used to verify the integrity of what files they were created for.

For a more detailed explanation of PAR files inner workings refer to the external links below.

External links

• Slyck's Guide to The Newsgroups - PAR filespropagation