DST 2007; A non-technical explanation

Significant effort has been put forth in the technical community to address, explain, and fix what’s going on relative to DST 2007. However, those of us that are non-technical would like to know what is happening, too! Following is my attempt at a simplified explanation for those of us that are non-technical end users and have questions about how Daylight Saving Time works inside computers.

It’s About Time
First, let’s discuss how our computers deal with time. The time we (humans) see on the computer is an “adjusted time” to be reflective of our respective time zone. It makes sense that the “displayed computer time” should be the same as the time indicated by the clocks on our walls. Otherwise, there would be serious difficulty in managing time! You think time management is difficult, now…

One Time
To unify the time used by computers, many computers synchronize their clocks as defined by GMT (Greenwich Mean Time) which is time on the Prime Meridian. To help eliminate confusion, I am going to refer to GMT as “zero-time” - the time used by computers to synchronize THEIR time. “Zero-time” on your machine is then visually adjusted and displayed in a format to be read by humans. For this discussion, let’s assume, too - that deep inside - ALL computers are synchronized to “zero-time” and your computer interface simply “adjusts” the “zero-time” into displayed time to make sense to the human user. (”Zero-time” is always “zero-time” regardless of where you are, what time zone you are in, or what computer you are using.)

Time Rules!
Now that we understand “zero-time,” let’s look at another complicating issue - when computer programs were written and what “rules” they were “taught.” An application written before August 2005 will adhere to the rules in place when it was written (old rules). An application written after August 2005 will have its rules in place reflective of the “new” DST schedules (new rules). It is within the rules defining the “visual adjustment” of “zero-time” to “displayed time” that the Daylight Saving Time issues begin.

My Time or Your Time?
Imagine you are using Windows XP (old rules) or Mac OSX (old rules) and you schedule an appointment with someone using Vista (new rules). Though both of these systems are synchronized to “zero time,” the “displayed computer time” is adjusted based on the rules of the operating system. The XP (old rules) or Mac (old rules) system will wait until April of 2007 to change its clock but Vista (new rules) will change its clock in March of 2007 – in compliance with the “new rules.” On a given day falling between “new rules” and “old rules” taking affect, one computer uses “zero-time”+8 hours (old rules) to adjust to the correct “displayed time” and the other uses “zero-time”+9 hours (new rules) to adjust for the “displayed time.” One of the systems is going to be off by an hour. Which one? Your guess is as good as mine on this one! But, we can rest assured that ONE computer will be out of synchronization until both systems adjust their displayed clocks. In the above example, both times would finally be synchronized in April when the “old rules” computer finally makes its adjustment and both machines are, once again, displaying the same time.

Time Off
This example of “old rules” and “new rules” is the basis for challenges concerning our PDAs, cell phones, laptop computers, mobile computing devices, ATMs, wrist watches, and your coffee maker that has a date and time set to brew your coffee in the morning just before you awake M-F, but not Saturday or Sunday. The devices mentioned previously use clocks and have the same “old rules/new rules” challenge.

Timely Information

Available Updates:
Updates and patches have been released by most companies that write software. Please understand that the “old rules” comparison used in connection with XP and OSX are for demonstrative use, only. Microsoft and Apple, respectively, have released updates to correct these synchronization issues. The most important way to alleviate any scheduling challenges is to ensure that ALL of your date-sensitive devices are updated to reflect the “new rules.”

What non-technical steps can I take to prevent an inconvenience?
Simply insert the time into the heading of the appointment, meeting, task, or whatever. By adding the time in the subject area, you can easily reference if something has gone awry during this transition. The subject line has nothing to do with the internal clock and it will not be affected by time change. The most critical windows to watch are the weeks that fall between the “old rules” and the “new rules” being enacted. This year, that time falls between March 11th and April 1st (no joke) and October 28th and November 4th.