Par2 Files Explained

Par2 Files are commonly used files on today's Usenet. They are not that common on the Internet in general and I can't think of a location where I encountered them except for the Usenet. Par2 Files can be used to repair broken rar archives. That is the basic explanation of course, the technical is a little bit more complicated. Lets use a example to make it clearer. Let us assume that you have downloaded a number of rar files (.rar, r01, r02 and so on) that can be unpacked to create the file test.avi which has a size of 700 Megabytes.

Let us further assume that some of the rar files have been uploaded incompletely to the Usenet which happens from time to time. Some of the files are corrupt so that you cannot extract the rar archive fully to play the movie afterwards because of the broken files.

Par2 Files are fixers. They analyze the blocks of each rar archive and can repair them if the need arises. Every Par2 file can be used to fix a certain number of blocks that corresponds to the number of blocks of rar files.

All you need to have is enough par2 files that can fix the missing blocks in the rar files to repair these files. The real beauty of this system is that you can fix any broken rar file with any par2 file. You do not need to look for the complete rar file, all you need is to download the par2 files which are normally posted with the rar files to the same newsgroup.

So, all you need are par files that can repair enough blocks to fix the rar archive so that it is fully repaired and can be extracted.

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I'm using the free software Quickpar to test and repair rar archives that I have downloaded from the Usenet.

par2 files explanation

The first screenshot shows the tested files using Quickpar. It shows that 96 blocks are missing and are needed to repair the archive so that it can be extracted. After downloading enough Par2 files to match the number of broken blocks, Quickpar automatically repairs the damaged files.



par2 files explanation

The second screenshot displays three par2 files that can be used to repair the damaged files. This process usually does not take more than a few minutes and you can extract the archive once the operation has been completed.

par2 files explanation

Some Usenet clients, like the excellent Newsbin Pro, support parity files natively so that you do not need another software program like Quickpar.

Two different Par versions are currently available, with a third in the making.

  • Par1 files are not really used that often anymore. They usually use the .p01, .p02 and so on file extension. The format is limited to 256 recovery files with each recovery file the size of the largest input file.
  • Par2 files improve the format in several aspects. First, you will notice that they always come with the .Par2 file extension and only differ in terms of file name. The files can have different file sizes and support up to 32768 recovery blocks.
  • Par3 is currently in development. The new format will support the inclusion of file folders in par archives and unicode support. The author of Multipar is currently working on that.

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Responses to Par2 Files Explained

  1. Dante May 4, 2007 at 3:31 am #

    I use the newsgroups (Usenet) extensively. And I have come to the conclusion that if someone's RAR posts are incomplete, their PAR posts are usually off kilter too. I find that it is generally a waste of time downloading incomplete RAR files. That's why I use the AndroidNews from http://www.sb-software.com/android/ as this program shows me if a RAR series is incomplete and I can just ignore it. Even with high speed 9mbps connection, it still take half an hour for some large programs to download. And trying to fiddle with RAR/PAR recovery afterwards is really really really annoying :(

  2. jaima March 11, 2008 at 3:57 am #

    i am with mewshosting.com 100 days retention and just about all my download have missing or incomplete rars, my latest download (6.80gb) had incomplete in every rar and all par2 were damaged, i had to bin the lot as i had 970 missing blocks, oh, and the files were only up 42 days.
    So much for paying a premium sever when you hagve to bin about half of your downloads, a waste of time and a waste of my money.
    forgot to mention when using binsearch it shows all files are there and i have 2 downloaders, Grabit and Newsleecher so i doubt that both the downloaders are faulty.

  3. Chris Knox April 25, 2008 at 3:26 pm #

    Par2 Files Explained
    I sort of understand the use of QuickPar but, using your example above, how do you now create the .avi file so you can view it?

  4. Martin April 25, 2008 at 3:56 pm #

    Chris the Par files are only there to assure file integrity. You unpack the files normally with an unpacker of your choice.

  5. JDonner November 11, 2008 at 12:20 am #

    I never use it for usenet, nobody wants to use that crap. I use it for backups on DVD, much more useful.

  6. taltamir August 9, 2009 at 2:05 pm #

    Dante and jaima are full of shit shills who are just pushing a paid for usenet service. Don't believe them. Even if some par files are corrupted and incomplete, as long as it is par2 it will have enough FRAGMENTS to repair.
    Not that paid for usenet service is bad, I use one (i will not mar my credibility by saying which one), but their claims about "unreliability" is BS

    Chris Knox, you right click on the .rar file and select "extract here". This process was to REPAIR the MISSSING rar files. Once you have them all it is standard unrar procedure.

    JDonner
    While it is useful on DVD, it is most commonly used on usenet... usenet is a favorite because it gives you maxed out download speed, usenet is the only practical way to max out a 20 mbps fios connection with a p2p download. But that means putting up with broken files and fixing them...

    Actually you can just get something like alt.binz and it will automatically download par files and automatically repair then automatically extract.

  7. migero December 29, 2009 at 12:54 pm #

    how do i know what par2 files get to repair rar parts ?

  8. gorditospree April 11, 2010 at 1:45 am #

    thanks so much!!!!!!!!

  9. Ed November 14, 2011 at 7:25 pm #

    Thanks gHacks

    Good program still.

    :)

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