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A question about file compression that is just out of curiosity...

Discussion in 'Support' started by mathewsdw, Mar 9, 2012.

  1. mathewsdw

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    and therefore not really all that important. Is the compression ratio (reported by the "c" field type in PDir, for example) based on the actual contents of the files (which really wouldn't make sense, it seems to me) or on the allocated size of the files (which does make sense)?

    - Dan
     
  2. thedave

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    IIRC it's based on the space allocated vs the actual size of the file expressed in a percentage.
     
  3. Steve Fabian

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    The method used by archiving software (*ZIP*, 7z, etc.) has no reference to space allocation; that could very based on cluster size. It is the ratio of compressed size to uncompressed size, because in an archive there is no dead space. For "disk compression" the compression reported ought to be the ratio of actually allocated space to allocation space required for the uncompressed file. For an uncompressed file which fits into a single cluster there is no space saving possible, it will always need that one cluster.
     

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