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[Help!] Alt+compare shows differences I can't see   [Help!]

By: Martijn Coppoolse   Homepage   Voorburg, NL  
Date: Feb 14,2019 at 04:19
In Response to: [Help!] Alt+compare shows differences I can't see (Peter Shute)

> Setting CO7A (ignore 2 second time difference) to Yes stopped it
> tagging files like this.
>
> Why does it think some similar looking times are different, but not
> others?

Do you know the filesystem on that storage medium? Some filesystems (I seem to recall FAT is one) store the timestamp(s) with reduced accuracy, up to 2 seconds*.

Simplifying a bit, this basically means every timestamp is rounded up or down to the nearest odd second. So all the files with an odd number of seconds in their original timestamp will keep their original timestamp, whereas files with an even number of seconds will be rounded, and therefore suddenly have a different timestamp, by up to 2 seconds.

I said this was simplified, because the timestamp is stored and rounded in a binary format; so it’s not always precisely even and odd seconds as displayed in 60-based decimal format. It will sometimes even happen that two binary timestamps are different, but their decimal representation is identical. I expect that ZTreeWin compares the binary representation (since that’s more efficient anyway), and so marks them as different.



* FAT date resolution:

  • 2 seconds for last modified time,
  • 10 ms for creation time,
  • 1 day for access date,
  • 2 seconds for deletion time
https://en.wikipedia.org/wiki/Design_of_the_FAT_file_system


--
Martijn

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