Re: Time change questions !

On 10/31/2006 11:46 AM, Richard B. Gilbert wrote:
JF Mezei wrote:
Stephen Hoffman wrote:

There are applications around which do not react appropriately when
the time changes -



However, when you consider that competing modern OS have automated,
sudden time changes, new applications, often written for such OS and
later ported to VMS, would have been written to handle such a sudden
time change.

If you have an old application being installed onto a fresh/new VMS
instance, then perhspas the onus should be on the system manager to
disable to automated time change. Wouldn't the vast majnority of apps
now survive a sudden time change ?

If you do financial transactions and you really do not want to have
transactions "back dated", then you need to a a lot to handle those time
changes and would have to be very aware of everything and disable the
SYSGEN AUTO_DLIGHT_SAV parameter (and possibly use some app that tweaks
the clock rate to slowly drift it to lose/gain an hour).

Modern O/Ss, including VMS, normally keep time in UTC. The display of local time is merely a convenience for the user. Each user, if he wishes, can have times displayed using his own local time zone. Time is thus always monotonically increasing, it's only the DISPLAY of the time that bounces around; time stamps should be unambiguous.

I'm sorry, this last paragraph is NOT TRUE for VMS.

VMS system time *is* the displayed time, no matter the timezone and/or
TDF settings. While there are various system services/LIB$/CRTL
routines to convert between system time and UTC, it is entirely
incorrect state that VMS uses UTC as the internal (system) time.

You can reason this out for yourself: a VMS quadword time is the number
of centiseconds since 17-NOV-1858. There is NO TIMEZONE information
carried in that definition. Data files (SYSUAF for example, but
database records as well) that store the time often do so as the
binary VMS quadword. Given the late arrival of UTC on VMS, it would
break backward compatibility to change the definition of that quadword
to be defined as UTC (and VMS Engineering doesn't do that...).

This does not mean you can't set the local timezone to GMT and avoid
the problems... It is actually a human factors problem rather than
a technical one (all the really hard problems seem to involve humans,
not machines!).

-Ken
--
I don't speak for Intel, Intel doesn't speak for me...

Ken Fairfield
D1C Automation VMS System Support
who: kenneth dot h dot fairfield
where: intel dot com
.

Relevant Pages

  • Re: Time change questions !
    ... If you have an old application being installed onto a fresh/new VMS ... disable to automated time change. ... Modern O/Ss, including VMS, normally keep time in UTC. ... Time is thus always monotonically increasing, it's only the DISPLAY of the time that bounces around; ...
    (comp.os.vms)
  • RE: Time change questions !
    ... Microsoft had problems with the time change affecting Meetings in Exchange ... later ported to VMS, would have been written to handle such a sudden ... If you have received the email in error, please notify TransGrid ... individual sender except where the sender expressly and with ...
    (comp.os.vms)
  • Re: Time change questions !
    ... disable to automated time change. ... If you do financial transactions and you really do not want to have ... Each user, if he wishes, can have times displayed using his own local time zone. ...
    (comp.os.vms)
  • Re: Time change questions !
    ... disable to automated time change. ... Wouldn't the vast majnority of apps ... If you do financial transactions and you really do not want to have ...
    (comp.os.vms)