Computer time resources

by Markus Kuhn

One of my side-line interests in computing are mechanisms and standards related to handling time, in particular conventional complications such as leap seconds and civilian time zones. This page is my bookmark list on the subject and also lists some work that I have done in this area.

Time basics

If you are not familiar with concepts such as leap seconds, TAI, UTC, UT1, then these brief introductory references will help you to get started:

Excellent more detailed tutorials on the definition of the various timescales are

Further information is available from various government and scientific organizations that handle the definition and dissemination of various aspects of time:


Leap seconds

Leap seconds were introduced in 1971 to reconcile astronomical time, which is based on the rotation on the earth, and physical time, which can me measured with amazing accuracy using atomic clocks.

An in-depth introduction into leap seconds, especially in the context of recent proposals to get rid of them, is

A consultation process has been underway since 1999, initiated by several international scientific organizations (ITU, URSI, IAU, etc.), to study whether the definition of UTC should be modified. In particular, it has been proposed to remove leap seconds from what is the basis of almost all regional civilian time zones, effectively decoupling civilian time keeping from the rotation of the earth. More information ...

Broadcast of standard time

UTC signals are made freely available via various forms of broadcast:

Application program interfaces

Computer programs access the clock managed by the operating systems via a standardized application program interface. Existing ones such as that provided in the ISO C and POSIX standards leave a lot to be desired, which motivated to write up a

that explores what a comprehensive clock interface for application programs could look like.

Further references

[This section needs a cleanup.]

Markus Kuhn

created 2003-07-01 – last modified 2003-08-12 –