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                    RAR Frequently Asked Questions (FAQ)

           Copyright 1994-99 Eugene Roshal.  All rights reserved.

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Published by Eugene Roshal with assistance from the users of RAR, UNRAR,
related utilities, and the RAR support sites.  This document may be freely
distributed for non-commercial and information purposes.  This document 
may not, under any circumstance, be traded, sold, or otherwise used for 
commercial gain or purposes without prior written consent of Eugene 
Roshal.
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Questions listed in this FAQ:
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Q: When I download a RAR archive using Netscape Navigator or communicator,
   the file is corrupt, what's wrong?

Q: RAR incorporates a number of different compression "methods", what are
   the advantages and disadvantages of using them and which one would you 
   recommend for daily use?

Q: I've heard a lot about "Solid" archives.  What are they and how can I use
   them?

Q: How could a user of my BBS (E-mail system, FTP server etc) extract
   files from RAR archives while RAR is shareware and one must register
   after a 40 day evaluation period?

Q: I failed to extract files from a solid multivolume RAR archive because
   one archive volume was damaged (bad floppy diskette). Help me!


Questions and Answers:
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Q: When I download a RAR archive using Netscape Navigator or Communicator,
   the file is corrupt, what's wrong?

A: Apache HTTP server erroneously reports the RAR archive type as
   text/plain and as a result, Netscape Navigator/Communicator treats
   the file as plain text.  To prevent this happening, those webmasters,
   who use Apache, should create .htaccess file in each directory which
   has RAR archives and add the following string to it:

   AddType application/x-rar-compressed rar

   If .htaccess already exists, this string should be added to the
   already existing file.
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Q: RAR incorporates a number of different compression "methods", what are
   the advantages and disadvantages of using them and which one would you 
   recommend for daily use?

A: RAR contains 6 different methods of compressing files, which one you 
   use would depend upon your requirements.  i.e. how much you demand the 
   file be compressed balanced against how much time you are willing to 
   devote to the compression process.  There is always a trade-off and the 
   final choice must be yours.  Our recommendation is to leave compression
   as "Normal" unless you have good reason to change it. 

     Store         No compression is used at all, the files are simply 
                   collected into the archive.  This method is quite fast
                   and is useful for simply copying files from one place 
                   to another.
     Fastest       The fastest compression method is applied.  This is
                   slower than the "store" method.
     Fast          A slightly better compression method is used, resulting
                   in a smaller file.
     Normal        A better compression method is used to achieve (almost)
                   optimal compression, at a slight cost in time.
     Good          A better compression method gains another increase of 
                   (0.1 - 0.3%) 
     Best          Uses the best compression method of all at the cost of
                   20% - 100% more time, for the purists only.

   Here are the results of a compression test:

    Method used   Time taken     %    Compressed size     %

       -m0           6.64      37.9       354262       100.00
       -m1          17.52     100.0       270534        76.37
       -m2          17.61     100.5       269431        76.05
       -m3          18.18     103.8       268314        75.74
       -m4          19.22     116.6       268123        75.68
       -m5          20.43     119.7       268091        75.68

   As you can see, as the packing method improves, the time required 
   increases, but the increase in time is proportionally much greater than 
   the gain acheived.  This why the default and recommended method is set
   to -m3    

   If you wish to obtain the 'ultimate' compression from RAR, without 
   regard for the time taken, then use -s -m5 -mde switches.

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Q: I've heard a lot about "Solid" archives.  What are they and how can I use
   them?

A: It has been well known, for a long time, that one method of increasing 
   the efficiency of compression, was to copy all the files to be compressed
   into a single file, before compressing them. This is called creating a
   "Solid" file before compressing. There are programs around which indeed
   perform this operation and act as a pre-processor to another archiver.
   RAR handles this function internally and invisibly to the user, it
   simply "sees" all files together as a single data stream, with the
   end result that the final output is significantly smaller than it would
   otherwise be.  The gain to be had from this type of archive can be
   significant and can be 10% - 60% of the size of the original archive.

   As with any other gain, there is a price to be paid and that price should 
   be taken into consideration before creating a "Solid" archive.  The best 
   way to understand if using a solid archive is best for you is to answer 
   the following questions:

   Q: How often are you going to update or modify the archive?

   A: Probably never       ..  Use a solid archive

      Rarely               ..  Use a solid archive

      Frequently           ..  Use a normal archive

   Q: Are you using RAR as a packer for an electronic mail system?

   A: Yes                  ..  Use a solid archive

   IMPORTANT NOTE:

   Beware that to extract a file from solid archive RAR scans the whole
   archive from the beginning.

   If you are using RAR to store archives to some unreliable storage media
   (e.g. floppy disks, streamer tapes etc.) you should better use normal,
   non solid mode. And you definetely should use the recovery option.

   It is impossible to extract files after damaged place in the solid
   archive. However in some cases special recovery information helps to
   rebuild the damaged archive if it is stored to the archive (the
   recovery option was on, the '-rr' switch or 'rr' command applied).

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Q: How could a user of my BBS (E-mail system, FTP server etc) extract
   files from RAR archives while RAR is shareware and one must register
   after a 40 day evaluation period?

A: The RAR distribution archive contains a free unRAR utility, unrar.exe,
   which can be used, without paying a license fee, by anyone wanting to 
   extract archives created by RAR.  As an additional BONUS to this, the 
   source code of a portable unRAR is available on www.rarlab.com

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Q: I failed to extract files from a solid multivolume RAR archive because
   one archive volume was damaged (bad floppy diskette). Help me!

A: First of all, you should use RAR recovery option (-rr) when storing
   archives onto not reliable media as the floppies are. Generally, it is 
   not recommended to create solid archives in this case, use the normal 
   (non solid) mode instead. You should be aware, that to extract files from
   a particular solid volume RAR scans the whole set of previous archive 
   volumes (.rar or .exe, .r00, .r01 etc).

   Steps of recovering process if you have damaged volume of solid archive:

   1) Try to repair the damaged volume (the 'r' option, 'repair' command).
      It helps sometimes if RAR recovery was used when creating archive.
      Rename recovered volume _recover.rar to the actual volume name and
      try to process your archive from the first volume to the newly
      recovered (if recovery were not used, RAR builds _reconst.rar).
      
   2) If previous procedure was not to any avail, then, unfortunately, 
      chances to restore files are reduced. You should have source files 
      contained in damaged volume (from the file where archive is broken
      upto the end of the volume). And, you should extract all files from
      all volumes until the CRC error in damaged place.

      Re-create volumes of the archive including damaged one, calling
      RAR with the same options and archiving all files in the same order 
      as when you created the archive for the first time. 

   If after that you are able to extract files from next volumes, you 
   should say a hundred times "Thank you, my Lord!! I will never use again 
   bad floppies, nor store multivolume solid archive to them without the
   recovery option when there is a bare suspicion (0.000000001 percent of 
   possibility) that the storage media is unreliable".
      
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end of file "RAR_faq.txt"

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