There have been allusions to computer systems other than POSIX which
recognize leap seconds. I thought I would point out a partial example of
one.
The z/Architecture Principles of Operation (descendant of the
System/370) explains in chapter 4 the operation of the time of day clock.
The publication is available at
http://www-01.ibm.com/support/docview.wss?uid=isg2b9de5f05a9d57819852571c500428f9a
One of the bits is incremented each SI microsecond, and the epoch is 1
January 1900 (sort-of UTC). Whole leap seconds are counted after 1
January 1972. Before that, the time scale considers every day to consist
of exactly 86,400 seconds. I found the explanatory text rather
confusing, and derived my impression of how it operates by examining the
values in the various tables.
I am not able to explain how the value of the time of day clock is
carried through programming libraries and finally displayed to people.
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