Since Usenet (also referred to as newsgroups) news servers place limits on how many lines they will accept, software (warez) and multimedia files (such as mp3, avi, and even DVD) are posted to the newsgroups by splitting the large files into an archive of smaller, compressed files. The problem with this is that one or more of the compressed files can end up being corrupted or not even be on the news server at all. Parchive files (PAR and PAR2) are the saving grace for this headache. Once downloaded, the parchive files for a selected archive can reconstruct missing or damaged files in that archive.
According to Wikipedia, PAR and PAR2 files are used to repair damaged files based on their binary pattern. If you want to read more on the topic, I highly suggest starting with their article.
Before you start experimenting with PAR and PAR2 files, download and install QuickPar.
Once QuickPar is installed, open it and click the Options button at the bottom of the application. In the Integration section, click the Associate with PAR files checkbox. This will allow you to easily use QuickPar for both PAR and PAR2 files.
Now go ahead and close QuickPar and start up your newsreader software (such as Forte Agent or GrabIt) and update the headers for your favorite binary newsgroup. After performing the update, you will be presented with (hopefully) a long list of various files on the server for that newsgroup. Our example will revolve around alt.binaries.freeware, but the steps will hold true for any of the binary newsgroups. If you take a closer look at the various lines, you will see some archives that are followed by a group of files with a PAR or PAR2 extension.
When parchive files are available for an archive, you should always include them in your download queue. You would never kick yourself for having them and not needing them but you’ll be throwing a fit if you need them and don’t have them. Imagine spending all day downloading an entire archive, only to find that one of the lines is missing or corrupt. To make matters worse, the server has removed the files. If you took my recommendation and downloaded the parchive files, then all is not lost.
Go to the directory that you save your downloaded newsgroup files. Double-click on one of the parchive files for the archive. QuickPar will scan the archive for damaged or missing lines. If you have enough recovery lines in your parchive files, QuickPar can rebuild the archive. Once it has finished scanning the archive, it should look like this:
However, if it doesn’t, check the AutoRepair checkbox. If you have the necessary amount of blocks in your parchive files, QuickPar will begin repairing the archive. Once it is finished, it will rescan the archive. If it shows that no repair is necessary, your archive is repaired and you can now use your compression software (such as WinRAR) to decompress the archive and get to the desired files.
