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"Introduction to Binary Newsgroups: Repairing Damaged or Missing Files" 
  02/01/2002

In the last article about binary newsgroups, we walked through the steps required to download and extract files in the popular formats like ACE and RAR. In this installment, we’re going to look at the ways in which you can repair a file that has been damaged during upload or is missing a file(s) that never made it to your news server.

As you already know, when you download binaries there will often be a large a number of files to download. If any files are missing or damaged, your extraction will be unable to finish, resulting in lost time and often aggravation if you cannot find another copy of the damaged or missing file. Another problem is that Winrar and Winace often do not disclose the nature of the error or even the actual file that is damaged or corrupted, making it difficult to track down the culprit. Luckily, there are several applications that are available to help you.

Many files posted to newsgroups are accompanied by an SFV (Simple File Validation) file. An SFV file is simply a list of CRC’s for for a given set of files. A CRC is a very special number that is generated using a series of mathematical equations. While you don’t need to concern yourself with how they are generated, you should understand that every file has a unique CRC. You can think of a CRC as an identifying fingerprint for a file. The CRC files are useful in determining if the files posted are exactly the same as the files uploaded by the sender. By using a third party program like Win-SFV32 (do a search on Yahoo or Google to find this free program), you can verify the contents of each of the files you download and locate any that are missing or damaged. This can save a great deal of time, and as we’ve already discovered, most of the time you’ll be unable to determine which file is damaged using only Winace or Winrar.

If you have been browsing through the binary newsgroups lately, you may have seen a file called a PAR file (short for Parity). These file are included with binary posts along with several files named File.P01, File.P02, etc. The PAR files should not be confused with a RAR file although you’ll soon understand why they are so valuable. First, PAR files are created by a program called Mirror (see www.wehlus.de/mirror for information and downloading of this free program). They are then posted along with the standard RAR or ACE files commonly used. Unlike RAR or ACE, you cannot use PAR files to simply extract data. Instead, PAR files are used for error correction and even detection if SFV is not also used. Using Mirror, you can repair damaged files or even replace completely missing files although there are some limits to its ability. For example, if you have a PAR file and three files named File.P01, File.P02 and File.P03, you can only replace or repair 3 files from the set of posted files. For example, if you are missing file File.R03 and have a damaged file named File.r10, you are in great shape. It’s a life saver for large downloads that often have damaged or missing files.

In the next installment, we’ll look at how you deal with the files that are left over after you extract them. The files will often have names such as ISO or BIN/CUE, and you will need third party tools to handle them. Good luck with your downloading.

 - by Clayton Crooks

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