In .NET, the following statements return different values:
Response.Write(
TimeZoneInfo.ConvertTime(
DateTime.Parse("2010-07-01 5:30:00.000"),
The difference is as follows:
Day Light Saving Time (DST) on the other hand is advancing clocks To and for with season changes, To make max use of day light.
"It is observed in many countries but not all". It might be variable, as last summer some countries like Pakistan, decided to bring back clocks a month later than they normally do.
World Time Zones is a good resource for up-to date time information around the globe.
Hope this helps