Your questions: are there two Windows updates for the new DST rules?
In reference to the information out there on product updates for the upcoming daylight saving time changes, Larry asks...
"Why are there two Windows updates for the new DST rules? Did the rules change after the first update was pushed?"
Short answer: yes, the rules changed. It turns out that assorted countries around the world try out or change to new DST rules, and even invent new time zones. These changes occur more times in a year than the-artist-formerly known-as-Prince has changed his name.
Longer answer: it can be a little complicated. There are changes to DST and time zones (TZ) that happen around the world that we may not be aware of, some that have been happening for years. Most applications look to Windows for this information. To keep up to date we have to continuously release new updates.
So, to your questions: In most cases, we're able to capture the worldwide updates in regular maintenance OS updates. But due to the number and timing, we're moving to a more regular cadence of shipping out semi-annual OS updates for DST and TZs. The two updates Larry mentions are the ones we issued this past Spring in North America (Feb '07) and more recently in August for the Fall Back changes.
After we released KB931836 (the February '07 time zone updates for the Windows OS), we saw changes in New Zealand (in April) and Jordan plus a few other changes. This resulted in KB 933360, the August '07 time zone Updates for the Windows OS. So technically, there will only be one current update roll-up of time zones and DST rules, which today is KB 933360.
There's an exception to every rule, of course... and this includes the countries that make changes annually. Take Brazil and Israel for a moment: there, the entry and exit dates (Spring Forward and Fall Back) change based on governmental decree and religious calendar, respectively. Some countries (and even individual states in the US) trial different times as Western Australia did a couple of years ago. And some change with very short notice (as Egypt just did - more on that below). I posted some general advice here.
And some countries decide on changes just weeks prior to the shift, as Egypt did in late August (with a shift just a couple of weeks later. I think that Venezuela's president will announce/ confirm changes tomorrow (Sunday, 16 Sept) in his weekly radio address, as noted here. In these cases, we have the option to release hotfixes for the impacted areas, which in some cases not all end users need apply to their systems. (Hotfix information for these countries: Egypt is KB940427, and Venezuela is KB938977.)
Now, add that a few applications and services don't reference the underlying OS for their TZ and DST rules (as we have with a few Microsoft products included on this list and some from third-parties) and you can see the complexity. We're working to improve the situation across the company and move more and more products and services to reference the OS, allowing Windows to maintain an up-to-date database listing of the current DST and TZ values.
As they say, watch this space for more details.