oh gosh!! is has been 7 days since i last update my blog.i din realize time passes so fast. Last Sunday which is 28/10 is DAYLIGHT SAVING DAY for the Europe and the western and north America.
(** what i got wikipedia)
n a typical case where a one-hour shift occurs at 02:00 local time, in spring the clock jumps forward from 02:00
standard time to 03:00 DST and the day has 23 hours, whereas in autumn the clock jumps backward from 02:00 DST to 01:00 standard time, repeating that hour, and the day has 25 hours. A digital display of local time does not read 02:00 exactly, but instead jumps from 01:59:59.9 either forward to 03:00:00.0 or backward to 01:00:00.0. In this example, a location observing
UTC+10 during standard time is at
UTC+11 during DST; conversely, a location at
UTC−10 during standard time is at
UTC−9 during DST.
Clock shifts are usually scheduled near a weekend midnight to lessen disruption to weekday schedules. A one-hour shift is customary, but Australia's Lord Howe Island uses a half-hour shift.[67] Twenty-minute and two-hour shifts have been used in the past.
Coordination strategies differ when adjacent time zones shift clocks. The European Union shifts all at once, at 01:00 UTC; for example, Eastern European Time is always one hour ahead of Central European Time.[59] Most of North America shifts at 02:00 local time, so adjacent zones do not shift simultaneously; for example, Mountain Time can be temporarily either zero or two hours ahead of Pacific Time. Australian districts go even further and do not always agree on start and end dates; for example, to start DST in 2006 Tasmania shifted clocks forward on 1 October, Western Australia on 3 December, and the remaining DST-observing areas on 29 October.[68]
Start and end dates vary with location and year. Since 1996 European Summer Time has been observed from the last Sunday in March to the last Sunday in October; previously the rules were not uniform across the European Union.[59] Starting in 2007, most of the United States and Canada observe DST from the second Sunday in March to the first Sunday in November,[69] yielding 34 weeks of DST every year, which is 65% of the year. The 2007 U.S. change was part of the Energy Policy Act of 2005; previously, from 1987 through 2006, the start and end dates were the first Sunday in April and the last Sunday in October, and Congress retains the right to go back to the previous dates once an energy-consumption study is done.[70]
Beginning and ending dates are the reverse in the southern hemisphere. For example, mainland Chile observes DST from the second Saturday in October to the second Saturday in March, with transitions at 24:00 local time.[71] The time difference between the United Kingdom and mainland Chile may therefore be three, four, or five hours, depending on the time of year.
Time zones often lie west of their idealized boundaries, resulting in year-round DST.
Argentina, western China, Iceland, and other areas skew time zones westward, in effect observing DST year round without complications from clock shifts. For example, Saskatoon, Saskatchewan is at 106°39′W longitude, slightly west of center of the idealized Mountain Time Zone (105°W), but Saskatchewan observes Central Standard Time (90°W) year-round so Saskatoon is always about 67 minutes ahead of mean solar time.[72] The United Kingdom and Ireland experimented with year-round DST from 1968 to 1971 but abandoned it because of its unpopularity, particularly in northern regions.[73]
Western France, Spain, and other areas skew time zones and shift clocks, in effect observing DST in winter with an extra hour in summer. For example, Nome, Alaska is at 165°24′W longitude, which is just west of center of the idealized Samoa Time Zone (165°W), but Nome observes Alaska Time (135°W) with DST, so it is slightly more than two hours ahead of the sun in winter and three in summer.[74]
DST is generally not observed near the equator, where sunrise times do not vary enough to justify it. Some countries observe it only in some regions; for example, southern Brazil observes it while equatorial Brazil does not.[75] Only a minority of the world's population uses DST because Asia and Africa generally do not observe it.
So what did the Microsoft did about in their PC?
This is what they have done.
As with zoneinfo, a user of Microsoft Windows configures DST by specifying the name of a location, and the operating system then consults a table of rule sets that must be updated when DST rules change. Procedures for specifying the name and updating the table vary with release. Updates are not issued for older versions of Microsoft Windows.[81] Windows Vista supports at most two start and end rules per time zone setting. In a Canadian location observing DST, a single Vista setting supports both 1987–2006 and post-2006 time stamps, but mishandles some older time stamps. Older Microsoft Windows systems usually store only a single start and end rule for each zone, so that the same Canadian setting reliably supports only post-2006 time stamps.[82]
These limitations have caused problems. For example, before 2005, DST in Israel varied each year and was skipped some years. Windows 95 used rules correct for 1995 only, causing problems in later years. In Windows 98 Microsoft gave up and marked Israel as not having DST, causing Israeli users to shift their computer clocks manually twice a year. The 2005 Israeli Daylight Saving Law established predictable rules but Windows zone files cannot represent the rules' dates in a year-independent way. Partial workarounds, which mishandle older time stamps, include manually switching zone files every year[83] and a Microsoft tool that switches zones automatically.
[84]
