Windows "date modified" and daylight savings time
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From: bucky3 on 2 Nov 2009 12:21 I just realized that now all my files' "Date Modified" are 1 hr off after daylight savings time. This is obvious when you compare the Date Modified vs EXIF date picture taken. After some research, I learned that the Date Modified timestamp is recorded in UTC. Then it is displayed with the current timezone adjustment. So before DST, if I had a file modified at 14:00 UTC, and my timezone was PDT(-7), then Windows file explorer would display the time stamp as 7:00, which was correct. But now that it is DST, which is PST(-8), Windows is displaying the time stamp as 6:00, which is incorrect. Is there a way to have Windows XP display the correct time stamp? I think it should take into account the date of the timestamp and figure out whether it was during DST or not. So a timestamp of 6/1/2009 14:00 would be adjusted -7:00 to 7:00 (since 6/1/2009 was during DST). Whereas a timestamp of 1/1/2009 14:00 would be adjusted -8:00 to 6:00 (since 1/1/2009 was not DST).
From: bucky3 on 2 Nov 2009 12:42 On Nov 2, 9:21 am, bucky3 <buc...(a)mail.com> wrote: > So before DST, if I had a file modified at 14:00 UTC, and > my timezone was PDT(-7), then Windows file explorer would display the > time stamp as 7:00, which was correct. But now that it is DST, which > is PST(-8), Windows is displaying the time stamp as 6:00, which is > incorrect. Correction: So *DURING* DST, if I had a file modified at 14:00 UTC, and my timezone was PDT(-7), then Windows file explorer would display the time stamp as 7:00, which was correct. But now that it is *NO LONGER* DST, which is PST(-8), Windows is displaying the time stamp as 6:00, which is incorrect.
From: David J Taylor on 2 Nov 2009 15:21 "bucky3" <bucky3(a)mail.com> wrote in message news:5072e4d8-79c4-4ffd-82a7-9ff4205ebbeb(a)u36g2000prn.googlegroups.com... > On Nov 2, 9:21 am, bucky3 <buc...(a)mail.com> wrote: >> So before DST, if I had a file modified at 14:00 UTC, and >> my timezone was PDT(-7), then Windows file explorer would display the >> time stamp as 7:00, which was correct. But now that it is DST, which >> is PST(-8), Windows is displaying the time stamp as 6:00, which is >> incorrect. > > Correction: > > So *DURING* DST, if I had a file modified at 14:00 UTC, and > my timezone was PDT(-7), then Windows file explorer would display the > time stamp as 7:00, which was correct. But now that it is *NO LONGER* > DST, which > is PST(-8), Windows is displaying the time stamp as 6:00, which is > incorrect. Why is it incorrect? The file was modified at a fixed time, to which is either added or not an hour. 06:00 normal time => 07:00 summer time. 14:00 - 8 hours => 06:00. If you always want "wall-clock" time displayed for files, store then on a FAT-16 file system. Possibly even a FAT-32 volume, but I haven't checked that. Cheers, David
From: Ofnuts on 2 Nov 2009 16:35 David J Taylor wrote: > > "bucky3" <bucky3(a)mail.com> wrote in message > news:5072e4d8-79c4-4ffd-82a7-9ff4205ebbeb(a)u36g2000prn.googlegroups.com... >> On Nov 2, 9:21 am, bucky3 <buc...(a)mail.com> wrote: >>> So before DST, if I had a file modified at 14:00 UTC, and >>> my timezone was PDT(-7), then Windows file explorer would display the >>> time stamp as 7:00, which was correct. But now that it is DST, which >>> is PST(-8), Windows is displaying the time stamp as 6:00, which is >>> incorrect. >> >> Correction: >> >> So *DURING* DST, if I had a file modified at 14:00 UTC, and >> my timezone was PDT(-7), then Windows file explorer would display the >> time stamp as 7:00, which was correct. But now that it is *NO LONGER* >> DST, which >> is PST(-8), Windows is displaying the time stamp as 6:00, which is >> incorrect. > > Why is it incorrect? The file was modified at a fixed time, to which is > either added or not an hour. 06:00 normal time => 07:00 summer time. > 14:00 - 8 hours => 06:00. You're both wrong :-) When going DST, you don't change timezones. You stay in the same timezone, but apply DST. In this time zone, June 21st, 12:00 is the way to denote a specific moment in time(*), and there is only one way to denote a specific moment in that time zone. If you went to lunch at 12:00 on that day, you aren't going to tell you went to lunch at 11:00 if you tell a story about it later in winter (unless it's used as an alibi and you are trying to fool a detective). So if a file has a June 21st 12:00 timestamp, the computer should always display it as June 21st 12:00 as long as it is set up in that time zone, whether DST applies or not. Of course, if the computer is configured in the next timezone, then the same timestamp can be displayed as June 21st, 11:00, and this will be the correct display in summer and winter in that time zone. So yes, Windows is broken (<http://www.peterdonis.net/computers/computersarticle3.html>), but what's new? (*) except for the "duplicate hour" that happens during the fallback night, -- Bertrand
From: David J Taylor on 2 Nov 2009 19:53
"Ofnuts" <> wrote in message news:4aef509d$0$12528$426a74cc(a)news.free.fr... [] > So if a file has a June 21st 12:00 timestamp, the computer should always > display it as June 21st 12:00 as long as it is set up in that time zone, > whether DST applies or not. Of course, if the computer is configured in > the next timezone, then the same timestamp can be displayed as June > 21st, 11:00, and this will be the correct display in summer and winter > in that time zone. [] > Bertrand Yes, I can see your argument, but if you take it to its logical conclusion, wouldn't you need to include the different time zone of the taking device in your calculation of displayed date as well as the time zone of the display device, so pictures taken at the same instant would show a different timestamp if they were taken in New York, London or Paris? Cheers, David |