Parchive

PAR1/PAR2 are Prüfsummenformate for files. For the creation as well as to test the Reed -Solomon code is used, which can detect and correct errors in reading or receiving digital data.

The file (s ) with checksums can (can not) be created from one or more output files. These are supplied internally patched virtual in so-called slices. The checksums are then formed in the same manner as PAR1, however. Not from the files, but from the slices Based on this, in addition to the actual data transmitted checksum ( file ( s) ) to check if the source files were transmitted without error, and if necessary replace any missing data or fix corrupted programs like Quickpar.

When creating PAR2 files can specify the size of the slices as well as the degree of redundancy. If too small a degree (much less than a slice ) can be no subsequent repair more. The total length of the PAR2 file (s ) they have no fixed ratio to the output files, and depends on the degree of redundancy. So it is possible to repair a 100 MB file using only a 1 MB PAR2 file - provided that there are errors only in a small area of the file on.

When a detected transmission errors in an output file at least one slice must be replaced, for which the corresponding recovery block is needed from a PAR2 file that typically contains several such blocks.

To repair a certain number of them is needed. The exact number may vary, so you can get the right combination of PAR2 files download specifically needed.

The file naming convention of a PAR2 file looks like this:

FFF is the starting index of existing in this file recovery blocks, NNN for their number. Thus, when 20 blocks are required recovery, there is the possibility of a PAR2 file with blocks 20, or, for example, to use 20 PAR2 files with one block.

Implementations

Quickpar is a Windows program that controls the creation, testing and repair of archive files with PAR2.

MULTIPAR is also a Windows program, but provides significantly more options than Quickpar and is also multi-core capable.

Par2 is the open - source implementation in the package par2cmdline. It is developed in the project parchive for Linux and Windows. A version with multi-threading exists.