Paul, There are some very erudite responses in this thread but I think I can deal with this query.
There is an absolute reference point for time[1] which deals with any adjustments the astronomers deem necessary and there are local conventions over how far a locality differs from this absolute reference. "Daylight Saving" belongs to the latter whereas "Leap Seconds" belongs to the former. Also all future "Leap Seconds" belongs to the former. Thus, if you do as I do with my PC, namely, get a "time fix"[2] every 24 hours or whenever I power on, the place you get your time from will inform you, as best it and the intervening network can, what the absolute reference time is and your PC will know how many hours[3] to add or subtract (approximately) to match what your wrist watch says. Checking your post again, I see that there is another issue which is knowing how to convert the number of very small time units since the midnight between the 31st December 1899 and 1st January 1900 into the absolute reference time. This is where knowing the fine details of where to insert future leap seconds comes in. Now I have to guess, but I expect that the clever astronomers predict the need for leap seconds sufficiently in advance - and have them internationally agreed - for the conversions built into z/OS or whatever to be adjusted as necessary for whatever releases/versions are current well in advance of the predicted time. I guess the paragraph above needs conformation from one of those erudite sources I mentioned. Chris Mason [1] A line on a hill overlooking the site of a Tudor palace on the Thames to the east of London where, since 1833, mariners in the vicinity on the river could reset their time pieces every day at one o'clock by observing a red ball drop on the roof of the observatory at the top of the hill. The modern way is SNTP. [2] Using a free SNTP utility, Dimension 4 ( www.thinkman.com ) and my reference is the local observatory. [3] I believe there are some parts of the world where 1/2 hour is considered appropriate. ----- Original Message ----- From: "Paul Gilmartin" <[EMAIL PROTECTED]> Newsgroups: bit.listserv.ibm-main To: <IBM-MAIN@BAMA.UA.EDU> Sent: Wednesday, 19 April, 2006 3:22 PM Subject: Re: TOD Clock the same as the BIOS clock in PCs? > In a recent note, john gilmore said: > > > Date: Tue, 18 Apr 2006 14:50:27 +0000 > > > > Two other IBM-supplied callable services are available: > > > > o STCKCONV converts arbitrary, in general non-current ETOD values into > > date-time ones; and > > > > o CONVTOD converts an STCKCONV date-time value [back] into an ETOD value. > > > > All three of these facilities make the necessary corrections for the > > peculiarities of the Grergorian calendar; the facilities they provide are > > comprehensive; and they should always be used in preference to homegrown > > conversion routines, which no non-specialist programmer ever gets right. > > > Do these likewise make the necessary corrections for Daylight Saving > Time and Leap Seconds? How do they deal with the uncertainty of > future leap seconds? > > -- gil > -- > StorageTek > INFORMATION made POWERFUL ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [EMAIL PROTECTED] with the message: GET IBM-MAIN INFO Search the archives at http://bama.ua.edu/archives/ibm-main.html
