Ever wonder what those files were? Well NewsgroupReviews will try to explain it in a simple, easy to understand tutorial. Some of those RAR files may be corrupt and the parity files are there to either fix the entire archive or just rebuild part of the archive. Certain RAR files are incomplete because something may have happened during the upload process to Usenet which affected their completion like a connection interrupted during upload, issues with propagating to Usenet correctly, etc.
When downloading a particular RAR archive you do not need to download the PAR2 files unless the file is obviously damaged. These files were used to verify the integrity of the RAR files that were uploaded to Usenet or allow for the recovery and reconstruction when a RAR file is incomplete or corrupted. Par1 files used the Reed-Solomon error correction method to create recovery files. They were the initial standard for repairing or reconstructing broken RAR files on Usenet.
Although PAR was a popular format and required less system resources, it suffered some limitations. PAR2 files — Howard Fukada specified that the new format work on the blocks of data that make up the RAR file instead of repairing the whole file. Programs like QuickPar can be used to open parity files and use them to check the integrity of the RAR file archives. To check a particular archive, download the smallest PAR2 of the set.
The file does not actually contain any recovery data, but it does allow you to test the integrity of the file. The first number is only significant in the case that you want to find a full set of PAR2 files. For example, let's say you have the following files: Filename. The second file starts at block 1 and contains 2 blocks. The third starts with block 3 and contains 4 blocks.
The fourth file starts with block 15 and contains 8 blocks. You can also conclude from the pattern in the filenames that a PAR2 file is missing, possibly named Filename.
Because the number of recover blocks are in the file name, you can actually download the file set, see how many blocks are needed, and then download at least that many recover blocks worth of PAR2 files.
Questions about Easynews? PAR2 somefile. Look at the PAR2 filenames above. If you needed seven blocks, then you could download the second and third PAR files. If you only needed two blocks, then you could just download the second file. PAR uses the Reed-Solomon algorithm.
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