Re: [LEAPSECS] Precise time over time

From: Poul-Henning Kamp <>
Date: Fri, 12 Aug 2005 09:21:51 +0200

In message <E1E3NBT-000440-00_at_grus.atnf.CSIRO.AU>, Mark Calabretta writes:

>However, the question that naturally arises is the required timescale
>of the extrapolation. A figure of 50 years seems first to have been
>suggested by Poul-Henning Kamp (Aug/04, "My personal opinion is that 50
>years seems right, 20 years might be livable") and since seems to have
>become set. However, I question the need for such a long extrapolation.

As I said, 50 years seems right, and it does so because there is
no currently running computer that has worked for 50 years.

Most electronics is considered unreliable for safety of life after
10-20 years and in general after about 30-40 years.

20 years might be livable because while there are computers which have
been running for more than 20 years, having to update a table for those
few systems might be livaable, but it does get us into the area where
long lived embedded systems need updates.

I know of far too many 15-20 year old systems still running, and
the way things are, I suspect I still know a lot of them in five
or ten years time, but then as 20 to 30 year old systems.

>I think
>the idea would be much more saleable with an initial timescale of, say,
>20 years, extended by 5 years every 5 years. So at any time the
>extrapolation would range between 15 and 20 years.

No, that is too short, 20-25 years _maybe_ but certainly no shorter
than that.

The only way we can compete economically with the existing proposal
is if we can make leapseconds a non-issue for all users, operators
and programmers and make them a concern for operting system programmers

For that to work, it needs to be such that you can deply a system
and not have to think about leapseconds for the lifetime of it. It
doesn't work if some of the programmers, operators or users need
to be aware of leapseconds and some don't, because then they all
need to be aware to tell if they in one or the other crowd.

It has to cover everybody until they are clearly aware that they
are running an antique computer and not just a trusty old computer.

In the US I belive something is antique when it is 25 years old,
in Europe I think it has to be 50 years old to gain the distinction.

So I think 50 years is the correct horizon.

Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk_at_FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Received on Fri Aug 12 2005 - 00:22:05 PDT

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