Something is going to happen next spring that hasn't happened since 1986 (back when the Energizer bunny first appeared, the Chicago Bears won the Super Bowl, and Nintendo introduced its games to America). The United States is changing when daylight saving time (DST) starts and ends. In 2007, DST will start three weeks earlier and end one week later.
Since 1986, DST has started on the first Sunday of April and ended on the last Sunday of October. Next year, because of the changes in the Energy Policy Act of 2005, DST is extended one month. It will begin on the second Sunday in March and end on the first Sunday of November.
The U.S. has changed the DST rules before. In fact, other countries around the world change DST rules often for many reasons. For example, Australia changed when DST ended in 2006 so that the time change would not occur in the middle of the Commonwealth Games. In addition to the U.S., Canada and Bermuda have decided to change their DST dates in 2007 to follow the same time zone rules.
A Little History on DST
The current U.S. law that sets DST is know as the Uniform Time Act of 1966. This law does not require that a state observe daylight saving time; all the law says is that if a state is going to observe daylight saving time, it must do so according to the terms of the Act. Several places—such as Arizona, Hawaii, and Guam—do not observe DST at all.
DST start and stop dates have changed several times in the history of the United States.
In order to conserve for the war effort in 1918, Congress placed the country on DST for the remainder of World War I. This law held for seven months during 1918 and 1919 but was so unpopular that it was repealed. In 1942, during World War II, Congress reinstated DST on February 9, 1942. It remained so until September 30, 1945. Between 1945 and 1966, different states had many different versions of DST. To resolve this, Congress established the Uniform Time Act of 1966, which created a standard DST (amended in 1986) to begin on the first Sunday of April and end on the last Sunday of October.
How Does This Impact You?
This change will impact not only the clock on your VCR (or TiVo for those of you who are more hip) but also your computers, including your System i and iSeries. I cannot explain how to correct your VCR, but I can explain how this change impacts your System i.
i5/OS has built-in support for time zones. The time zone system value (QTIMZON) specifies the name of the time zone description that is used to calculate local system time. To reflect this DST change in i5/OS, the system simply needs to be told what the new rules are.
How Does i5/OS Support Time Zones?
i5/OS supports time zones through the QTIMZON system value and a set of time zone objects you can set QTIMZON to. For example, if I want to set my system to my time zone in Rochester, Minnesota, I would set QTIMZON to use "QN0600CST". This value indicates that my system should use the Central Standard Time (CST) and Central Daylight Time (CDT) rules. You can see what the provided values mean by going to the Information Center.
You can also create your own time zone object (but there is no need to do this in the United States), in which you specify the offset from UTC, the Standard Time names, the DST names, and the DST start and end rules. If you do create one, you should give it a name that doesn't start with Q since that's what the IBM-provided ones start with.
What Releases Is IBM Fixing?
IBM is fixing V5R3M0 and V5R4M0, earlier releases are not being updated because automatic DST support was first added in V5R3M0.
What happens if you don't update the system? Essentially, the system time will be incorrect for four weeks next year because it will be using the old DST rules. This could cause all kinds of issues to your users. These problems could be as benign as incorrect times on reports or as bad as failure of critical applications. For example, suppose your system disables access on the shipping dock station each day at 5:00 p.m. Suddenly, on Monday, your system will disable access at 4:00 p.m., so nothing will ship out of the dock that last hour of the day.
The Solution
IBM implemented two updates to address this change.
The first update was to release PTFs (SI24716 for V5R3M0 and SI24717 for V5R4M0) on August 1, 2006, that are designed for testing. They provide the new U.S. time zone objects that support the DST changes. Customers can activate and deactivate the new DST support anytime after the PTF is applied by changing the QTIMZON system value to have the new name. For more information on the exact changes needed, see the cover letters. (Note: Production systems should not activate this change.)
The second update, which will be released on November 13, 2006, automates the changes needed to support the new DST information. The fix will be released before Thanksgiving, so customers will have the opportunity to install it if they have a maintenance window over that weekend. Once this PTF (SI24906 for V5R3M0 and SI24908 for V5R4M0) is loaded and installed on a system, the new DST rules will be in effect. This PTF is immediate and will not require a system IPL. You can install it at any time that is convenient (but before March 2007!).
This automatic update will change the system value to the new rules only if the system is using one of IBM's shipped *TIMZON objects and if that object refers to a time zone that has been impacted by the new DST rules. This should be the normal case for U.S. customers. If the *TIMZON object referenced has been modified or is user-defined, the PTF will not update the value.
If you want to view the time zone properties on your system, you can use iSeries Navigator. You simply expand My Connections -> server-name -> Configuration and Service -> Time Management -> Time Zones. See Figure 1.
Figure 1: Use iSeries Navigator to view the time zone properties on your system. (Click image to enlarge.)
You can then use the Time Zones dialog box to verify that the time zone specified in the Current time zone system value field is the new value specified in the PTF cover letter. Click here for more information on System i time support.
IBM recommends that you do not edit the IBM-provided time zone object because doing so will deactivate the automatic update support due out in November.
In addition to the information mentioned previously, IBM has implemented a new DST2007 keyword in RETAIN. This new common keyword has been implemented to help customers and IBM Service teams find relevant DST information across all products.
You can find out more about time zones and DST at the links below:
• http://en.wikipedia.org/wiki/Time_zone
• http://www.worldtimezone.com/daylight.html
• http://wwp.greenwichmeantime.com/time-zone/usa/
And by the way, don't forget to set your clocks back on Sunday, October 29!
Pat Glenski is the i5/ OS Globalization Architect for IBM in Rochester,
Minnesota. He is responsible for the system support of internationalization and
globalization on the IBM System i family. Pat has worked in the area of software globalization for over 10 years. He has presented at COMMON and several other conferences on the topics of globalization, global software development, testing global software, character encodings, and Unicode. He has been an advisor for several customers on how to extend their existing applications with Unicode support. Pat has worked on globalization issues and design for i5/ OS, Linux,Microsoft Windows, Java, AIX 5L, Domino, and many other projects. Pat has patents and other papers in this area.
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