Y2K38 Watch Starts Saturday

Jon Masters writes "I just wanted to remind everyone that Saturday, January 19th 2008 will mark the beginning of the 30-year countdown to the Y2K38 bug, when Unix time will overflow 32 bits. Some 30-year loan calculation software might start having problems with this over the weekend."

Comments

Re:Unix is made of *FAIL*

[ewilts]

> VMS has been Y10K-compliant for over a decade.

It's much better than that. It's mostly DCL that has the year 9999 issue. For those of you who like history lessons and how to design real operating systems (and customer support, back when it actually existed), read this article:

  38 Why Is Wednesday November 17, 1858 The Base Time For VAX/VMS?

COMPONENT: SYSTEM TIME OP/SYS: VMS, Version 4.n

LAST TECHNICAL REVIEW: 06-APR-1988

SOURCE: Customer Support Center/Colorado Springs

QUESTION:

Why is Wednesday, November 17, 1858 the base time for VAX/VMS?

ANSWER:

November 17, 1858 is the base of the Modified Julian Day system.

The original Julian Day (JD) is used by astronomers and expressed in days
since noon January 1, 4713 B.C. This measure of time was introduced by
Joseph Scaliger in the 16th century. It is named in honor of his father,
Julius Caesar Scaliger (note that this Julian Day is different from the
Julian calendar named for the Roman Emperor Julius Caesar!).

Why 4713 BC? Scaliger traced three time cycles and found that they were
all in the first year of their cyle in 4713 B.C. The three cycles are 15,
19, and 28 years long. By multiplying these three numbers (15 * 19 * 28
= 7980), he was able to represent any date from 4713 B.C. through 3267 A.D.
The starting year was before any historical event known to him. In fact,
the Jewish calendar marks the start of the world as 3761 B.C. Today his
numbering scheme is still used by astronomers to avoid the difficulties of
converting the months of different calendars in use during different eras.

So why 1858? The Julian Day 2,400,000 just happens to be November 17, 1858.
The Modified Julian Day uses the following formula:

      MJD = JD - 2,400,000.5

The .5 changed when the day starts. Astronomers had considered it more
convenient to have their day start at noon so that nighttime observation times
fall in the middle. But they changed to conform to the commercial day.

The Modified Julian Day was adopted by the Smithsonian Astrophysical Obser-
vatory (SAO) in 1957 for satellite tracking. SAO started tracking satellites
with an 8K (non-virtual) 36-bit IBM 704 computer in 1957, when Sputnik was
launched. The Julian day was 2,435,839 on January 1, 1957. This is
11,225,377 in octal notation, which was too big to fit into an 18-bit field
(half of its standard 36-bit word). And, with only 8K of memory, no one
wanted to waste the 14 bits left over by keeping the Julian Day in its own
36-bit word. However, they also needed to track hours and minutes, for which
18 bits gave enough accuracy. So, they decided to keep the number of days in
the left 18 bits and the hours and minutes in the right 18 bits of a word.

Eighteen bits would allow the Modified Julian Day (the SAO day) to grow as
large as 262,143 ((2 ** 18) - 1). From Nov. 17, 1858, this allowed for seven
centuries. Using only 17 bits, the date could possibly grow only as large as
131,071, but this still covers 3 centuries, as well as leaving the possibility
of representing negative time. The year 1858 preceded the oldest star catalog
in use at SAO, which also avoided having to use negative time in any of the
satellite tracking calculations.

This base time of Nov. 17, 1858 has since been used by TOPS-10, TOPS-20, and
VAX/VMS. Given this base date, the 100 nanosecond granularity implemented
within VAX/VMS, and the 63-bit absolute time representation (the sign bit must
be clear), VMS should have no trouble with time until:

      31-JUL-31086 02:48:05.47

At this time, all clocks and time-keeping operations within VMS will suddenly
stop, as system time values go negative.

Note that all time display and manipulation routines within VMS allow for
only 4 digits within the 'YEAR' field. We expect this to be corrected in
a future release of VAX/VMS sometime prior to 31-DEC-9999.

Re:What about the new 40 and 50 year loans?

[jandrese]

That and most of the Y2K problems were just display errors, not bugs in the actual calculations going on under the scenes. 2038 is much scarier and is a lot more difficult to fix. In fact the best way to fix the problem is probably to switch to a 64 bit representation of time, but thus far not too many people have made moves in that direction. Switching to 64 bits is not as easy as it might sound either, since lots of programs use timestamps and many of them make assumptions as to the size of their time fields. I do wish APIs would start to get transition structures (time_t64 or something) in place that people could start using now. If you do it early enough you can save yourself a lot of headaches down the road.

The big problem of course is that most people figure their code won't be in use in 2038 and don't care. I'll be right about retirement age by then. Crap, I just realized I'm going to be the grizzled old guy they call when this problem finally rolls around. One of those crusty old farts that knows C (just like the crusty COBOL farts that got a lot of jobs back in 1999 for a few months).