Re: [LEAPSECS] The real problem with leap seconds

From: Tim Shepard <shep_at_ALUM.MIT.EDU>
Date: Mon, 09 Jan 2006 19:33:47 -0500

> >and you still cannot even get it [TAI] reliably from your
> >average local NTP server.
> This is a circular argument: The reason NTP doesn't provide it
> is that time_t needs UTC.

No, I asked David Mills about 15 or so years ago why NTP distributes
UTC and not TAI (me thinking and suggesting that it would have been so
much better if NTP distributed TAI) and the reason was quite simple:

There was no convenient way to get TAI. The time signals broadcast by
WWV and WWVB in the US distributed UTC and leap warning bits, but did
not distribute (and still do not AFAIK) what the TAI offset is.

GPS receivers were (very) rare back then, so getting GPS time and
subtracting out the constant offset to get back to TAI was not a
viable option either (though perhaps it would be today, as long as the
GPS system keeps running).

I still think NTP should have distribute TAI, but I understand using
TAI was not practicable option when NTP was designed.

BTW, I don't know if the Fuzzball OS had any Posix time_t's in it, or
anything resembling them, but I suspect not. I vaguely recall hearing
that it had some other way of keeping the time in a collection of
16-bit registers (PDP-11s, don't you know).

                        -Tim Shepard
Received on Mon Jan 09 2006 - 16:45:00 PST

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