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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
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<H2 CLASS="western" STYLE="font-style: normal"><FONT FACE="Tahoma, sans-serif">Daylight
saving time <SPAN STYLE="font-weight: normal">(Windows)</SPAN></FONT></H2>
<P STYLE="margin-bottom: 0cm"><BR>
</P>
<P STYLE="margin-bottom: 0cm"><FONT FACE="Tahoma, sans-serif">A
common problem synchronization software has to deal with are +-1 hour
file time shifts after a Daylight Saving Time (DST) switch has
occurred. This can be observed for example when a FAT-formatted
volume is compared against an NTFS volume as frequently happening
with USB memory sticks. Files that previously appeared to be in sync
are now shown with an one hour modification time offset, although
they have not been modified by the user or by other means.</FONT></P>
<P STYLE="margin-bottom: 0cm"><FONT FACE="Tahoma, sans-serif">The
reason for this strange behavior lies in the way NTFS and FAT drives
store file times: NTFS stores time in UTC format, while FAT uses
local time.</FONT></P>
<P STYLE="margin-bottom: 0cm"><FONT FACE="Tahoma, sans-serif">When
times stored in these two different formats are compared, one format
has to be converted into the other first. In both cases Windows uses
the current DST status as well as current time zone information for
its calculations. Consequently the result of this comparison is
dependent from current system settings and in particular file times
that used to be the same can show up as different after a DST switch.</FONT></P>
<P STYLE="margin-bottom: 0cm"><BR>
</P>
<P STYLE="margin-bottom: 0cm"><FONT FACE="Tahoma, sans-serif">For a
detailed discussion about this issue refer to:
<A HREF="http://www.codeproject.com/KB/datetime/dstbugs.aspx">http://www.codeproject.com/KB/datetime/dstbugs.aspx</A></FONT></P>
<P STYLE="margin-bottom: 0cm"><BR>
</P>
<P STYLE="margin-bottom: 0cm"><FONT FACE="Tahoma, sans-serif"><B>Solution:</B></FONT></P>
<P STYLE="margin-bottom: 0cm"><FONT FACE="Tahoma, sans-serif">Luckily
FreeFileSync users need not to worry about this issue. Each file on a
FAT volume automatically gets additional meta data encoded in its
creation date that enables a correct file time calculation. This not
only solves all DST issues but also time shifts that occur due to
travel between different time zones.</FONT></P>
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</P>
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