Compression discrepancies (v4.57)
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#833 Compression discrepancies (v4.57)
In theory, selecting "Add to archive..." and using the default normal compression scheme should produce the exact same output file as selecting "Add to filename.7z" from the context menu. However, this doesn't seem to be the case; I noticed that selecting the second option ("Add to filename.7z") produces a slightly smaller archive (4,268,015 vs. 4,269,691 bytes in my case).
Does anyone know why there is this discrepancy, and if it's really a bug, or are the two options using different compression settings internally?
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When 7-zip scans folder, it can change Access_Time for some files (and Modification_Time for folders). So archive headers can be slightly different.
Check total sizes with "list" command:
7z l a1.7z > a1.txt
7z l a2.7z > a2.txt