In computer science, time formatting and storage bugs are a class of software bugs which may cause time and date calculation or display to be improperly handled. These are most commonly manifestations of arithmetic overflow, but can also be the result of other issues. The most well-known consequence of bugs of this type is the Y2K problem,
but many other milestone dates or times exist that have caused or will
cause problems depending on various programming deficiencies.
Year 1970
During
the 1960s, some computer programs were written using just a single
digit for the year, so that 0–9 represented the years 1960–1969. It was
especially easy to write programs in the COBOL
language with this limitation. While many companies identified this
problem in advance, some did not and outages occurred when the decade
rolled over. The fix generally was to expand the year to just two
digits, owing to limitations of the storage media common in that era,
tab cards and magnetic tape.
Year 1975
On 4 January 1975, the 12-bit field that had been used for dates in the Decsystem 10
operating systems overflowed. There were numerous problems and crashes
related to this bug while an alternative format was developed.
Year 1977
- 4 bits for the month
- 5 bits for the date therein
- 3 bits for the year.
This was recognized when COS-310 was developed, and dates were recorded differently.
Year 1989
Some
mainframe programs were written to encode dates as the number of days
since a 'zero date' of 1 January 1900, storing them as signed 16-bit
binary integers. On 18 September 1989, these programs began to fail, the
date being exactly 32,768 (215) days since the zero date.
Values on and after this day do not fit into a signed 16-bit integer,
but overflow and return negative values.
Year 1997
The Domain/OS
clock, which is based on the number of 4-microsecond units that has
occurred since 1 January 1980, rolled past 47 bits on 2 November 1997,
rendering unpatched systems unusable.
Year 1999
In
the last few months before the year 2000, two other date-related
milestones occurred that received less publicity than the then-impending
Y2K problem.
First GPS rollover
GPS dates are expressed as a week number and a day-of-week number, with the week number transmitted as a ten-bit value. This means that every 1024 weeks (about 19.6 years) after Sunday 6 January 1980 (the GPS epoch), the date resets again to that date; this happened for the first time at 23:59:47 on Saturday 21 August 1999, the second time at 23:59:42 UTC on 6 April 2019, and will happen again on 20 November 2038.
To address this concern, modernised GPS navigation messages use a
13-bit field, which only repeats every 8,192 weeks (157 years), and will
not return to zero until near the year 2137.
9/9/99
In many programs or data sets, "9/9/99" was used as a rogue value
to indicate either an unresolved date or as a terminator to indicate no
further data was in the set. This raised issues upon the arrival of the
actual date this represents, 9 September 1999.
Year 2000
Two-digit year representations
Follow-on problems caused by certain temporary fixes to the Y2K
problem will crop up at various points in the 21st century. Some
programs were made Y2K-compliant by continuing to use two digit years,
but picking an arbitrary year prior to which those years are interpreted
as 20xx, and after which are interpreted as 19xx.
For example, a program may have been changed so that it treats
two-digit year values 00–68 as referring to 2000 through 2068, and
values 69–99 as referring to 1969 through 1999. Such a program will not be able to correctly deal with years beyond 2068.
For applications required to calculate the birth year (or another
past year), such an algorithm has long been used to overcome the Year 1900 problem, but it has failed to recognise people over 100 years old.
Year 2010
Some
systems had problems once the year rolled over to 2010. This was dubbed
by some in the media as the "Y2K+10" or "Y2.01k" problem.
The main source of problems was confusion between hexadecimal number encoding and BCD encodings of numbers. The numbers 0 through 9 are encoded in both hexadecimal and BCD as 0016 through 0916. But the decimal number 10 is encoded in hexadecimal as 0A16 and in BCD as 1016. Thus a BCD 1016 interpreted as a hexadecimal encoding erroneously represents the decimal number 16.
For example, the SMS
protocol uses BCD encoding for dates, so some mobile phone software
incorrectly reported dates of messages as 2016 instead of 2010. Windows Mobile
was the first software reported to have been affected by this glitch;
in some cases WM6 changed the date of any incoming SMS message sent
after 1 January 2010 from the year 2010 to 2016.
Other systems affected include EFTPOS terminals, and the PlayStation 3 (except the Slim model).
The most important such glitch occurred in Germany, where upwards
of 20 million bank cards became unusable, and with Citibank Belgium,
whose digipass customer identification chips stopped working.
Year 2011
Taiwan officially uses the Minguo calendar, which considers the Gregorian year 1912 to be its year 1. Thus, the Gregorian year 2011 is the ROC year 100, its first 3-digit year.
Year 2013
The unmanned Deep Impact spaceprobe lost communication with Earth on 11 August 2013, after a clock counted 232 deciseconds (tenths of seconds) since 1 January 2000.
Year 2019
Second GPS rollover
GPS dates are expressed as a week number and a day-of-week number, with the week number transmitted as a ten-bit value. This means that every 1024 weeks (about 19.6 years) after Sunday 6 January 1980 (the GPS epoch), the date resets again to that date; this happened for the first time at 23:59:47 on Saturday 21 August 1999, the second time at 23:59:42 UTC on 6 April 2019, and will happen again on 20 November 2038.
To address this concern, modernised GPS navigation messages use a
13-bit field, which only repeats every 8,192 weeks (157 years), and will
not return to zero until near the year 2137.
Japanese calendar transition
On 30 April 2019, Emperor Akihito of Japan abdicated favoring his son Naruhito. As years in Japan are traditionally referred to by era names that correspond to the reign of each emperor, this resulted in a new era name, Reiwa (令和), following Naruhito's accession to the throne the following day. Because the previous emperor, Hirohito,
died in 1989 and Akihito's reign mostly corresponded with the rise in
the use of computers, most software had not been tested to ensure
correct behavior on an era change. Furthermore, testing was complicated
by the fact that the new era name was not revealed until April 1, 2019.
Therefore, errors were expected from software that did not anticipate a
new era.
Classic Mac OS
The
control panel in Classic Mac OS versions 6, 7, and 8 only allows the
date to be set as high as December 31, 2019, although the system is able
to continue to advance time beyond that date.
Year 2020
WWE 2K20 and Star Wars Jedi: Fallen Order
would both crash on January 1, 2020, when the year rolled over. The
glitches could only be circumvented by resetting the year back to 2019
until a patch was released. Additionally, Crystal Reports 8.5 would fail to generate specific reports starting in 2020.
Parkeon
parking meters in New York City and other locations were unable to
accept credit cards as a form of payment starting in 2020. A workaround
was implemented, but required each meter to be individually updated. In
New York, the meters were not expected to be fixed until January 9th.
In Poland, 5,000 cash registers stopped printing the date out properly.
SUUNTO sport smart watches showed out an error in computing week
days, that was presented with a +2 step (aka: FRI rather WED, SAT rather
than THU). For SUUNTO Spartan model watches, bug was fixed with
firmware release 2.8.32.
Year 2028
During
the late 1970s, on Data General Nova and Eclipse systems, World
Computer Corporation (doing credit union applications) created this date
format;
16-bit date field:
- 128 years = 7 bits (1900+128=2028)
- 12 months = 4 bits
- 31 days = 5 bits
Dates were directly comparable using unsigned functions.
No known instances of this format are in use today.
Year 2031
Palm OS uses both signed integers with the 1970 epoch, as well as unsigned integers with the 1904 epoch, for different system functions, such as for system clock, and file dates (see PDB format). While this should result in Palm OS being susceptible to the 2038 problem,
Palm OS also uses a 7-bit field for storing the year value, with a
different epoch counting from 1904, resulting in a maximum year of
(1904+127) 2031.
Year 2036
The Network Time Protocol has an overflow issue related to the Year 2038 problem,
which manifests itself at 06:28:16 UTC on 7 February 2036, rather than
2038. The 64-bit timestamps used by NTP consist of a 32-bit part for
seconds and a 32-bit part for fractional second, giving NTP a time scale
that rolls over every 232 seconds (136 years) and a theoretical resolution of 2−32
second (233 picoseconds). NTP uses an epoch of 1 January 1900. The
first rollover occurs in 2036, prior to the UNIX year 2038 problem.
Year 2038
Unix time rollover
The original implementation of the Unix operating system stored system time as a 32-bit signed integer representing the number of seconds past the Unix epoch:
midnight UTC, 1 January 1970. This value will roll over on 19 January
2038. This problem has been addressed in most modern Unix and Unix-like
operating systems by storing system time as a 64-bit signed integer,
although individual applications, protocols, and file formats will still
need to be changed as well.
DVB rollover
The Digital Video Broadcast system has an issue on 22 April 2038, when the 16 bits used to transmit Modified Julian Days used for electronic guide scheduling will restart from zero. The ETSI
EN 300 368 specification mentions in Annex C that the provided MJD
formulas are valid until 28 February 2100, but makes no mention of the
limits imposed by the 16 bits used to transmit the resulting value.
Third GPS rollover
GPS dates are expressed as a week number and a day-of-week number, with the week number transmitted as a ten-bit value. This means that every 1024 weeks (about 19.6 years) after Sunday 6 January 1980 (the GPS epoch), the date resets again to that date; this happened for the first time at 23:59:47 on Saturday 21 August 1999, the second time at 23:59:42 UTC on 6 April 2019, and will happen again on 20 November 2038.
To address this concern, modernised GPS navigation messages use a
13-bit field, which only repeats every 8,192 weeks (157 years), and will
not return to zero until near the year 2137.
Year 2040
Early Apple Macintosh computers store time in their real-time clocks (RTCs) and HFS
filesystems as an unsigned 32-bit number of seconds since 00:00:00 on 1
January 1904. After 06:28:15 on 6 February 2040, this will wrap around
to 1904. HFS+, the default format for all of Apple's recent Macintosh computers, is also affected. The replacement Apple File System resolves this issue.
ProDOS for the Apple II
computers only supports two-digit year numbers. To avoid Y2K issues,
Apple issued a technical note stating that the year number was to
represent 1940-2039.
Software for the platform may incorrectly display dates beginning in
2040. A third-party effort is underway to update ProDOS and application
software to support years up to 2924.
Year 2042
On 18 September 2042, the Time of Day Clock (TODC) on the S/370 IBM mainframe and its successors, including the current zSeries, will roll over. The UTC time will be a few seconds earlier, due to leap seconds.
Older TODCs were implemented as a 64-bit count of 2−12 microsecond (0.244 ns) units, and the standard base was 1 January 1900 UT.
In July 1999 the extended TODC clock was announced, which extended the
clock to the right (that is, the extended bits are less significant than
the original bits). The actual resolution depends on the model, but
the format is consistent, and will, therefore, roll over after 252 microseconds.
The TODC value is accessible to user mode programs and is often used for timing and for generating unique IDs for events.
While IBM has defined and implemented a longer (128-bit) hardware
format on recent machines, which extends the timer on both ends by at
least 8 additional bits, many programs continue to rely on the 64-bit
format which remains as an accessible subset of the longer timer.
Year 2048
The ATSC
system will have an issue similar to the DVB issue described above
after 2048 due to its use of signed 32-bit GPS seconds that begin from 6
January 1980.
The capacity planning logic in the ERP system SAP S/4HANA
supports only finish dates up to 19 January 2048 (24855 days from 1
January 1980). This concerns e.g. the production, maintenance and
inspection planning.
Year 2050
Various Texas Instruments calculators of the TI BA II Plus, TI BA II Plus Professional, TI-83, TI-84 and NSpire families support a function named dbd
to calculate the number of days between dates. This function accepts
dates between 1950-01-01 and 2049-12-31 only. One potential area where
this will start causing problems in 2020 is in the calculation of
30-year mortgages.
Year 2079
Days 32,768 and 65,536
Programs that store dates as the number of days since an arbitrary date (or epoch)
are vulnerable to roll-over or wrap-around effects if the values are
not wide enough to allow the date values to span a large enough time
range expected for the application. Signed 16-bit binary values roll
over after 32,768 (215) days from the epoch date, producing
negative values. Some mainframe systems experienced software failures
because they had encoded dates as the number of days since 1 January
1900, which produced unexpected negative day numbers on the roll-over
date of 18 September 1989. Similarly, unsigned 16-bit binary days counts
overflow after 65,536 (216) days, which are truncated to zero values. For software using an epoch of 1 January 1900, this will occur on 6 June 2079.
Year 2080
Some (if not all) Nokia phones that run Series 40 (such as the Nokia X2-00)
only supports dates up to 2079-12-31 and will refuse to change dates
further than 2079-12-31. The workaround is to use the year 1996 in lieu
of 2080 as a compatible leap year to display the correct day of the
week, date and month on the main screen.
Systems storing the year as a two-digit value 00..99 internally
only (like many RTCs) may rollover from 2079-12-31 to the IBM PC and DOS
epoch of 1980-01-01.
Year 2100
DOS and Windows file date API and conversion functions (such as INT 21h/AH=2Ah) officially support dates up to 2099-12-31 only (even though the underlying FAT filesystem
would theoretically support dates up to 2107). Hence, DOS-based
operating systems as well as applications that convert other formats to
the FAT/DOS format, may show unexpected behavior starting 2100-01-01.
Another problem will emerge at the end of 2100-02-28, since 2100 is not a leap year,
whereas many common implementations of the leap year algorithm are
incomplete or simplified, and thus will erroneously assume it to be a
leap year. This would cause the date to incorrectly roll over from
2100-02-28 to 2100-02-29, instead of directly to 2100-03-01.
Year 2106
Many existing file formats, communications protocols, and application interfaces employ a variant of the Unix
time_t date format, storing the number of seconds since the Unix Epoch (midnight UTC, 1 January 1970) as an unsigned
32-bit binary integer. This value will roll over on 7 February 2106 at
06:28:15. That is, at this time the number of seconds since 01 January
1970 is FFFF FFFF in hex.
(This storage representation problem is independent of programs
that internally store and operate on system times as 64-bit signed
integer values.)
Year 2108
The date timestamps stored in FAT filesystems, originally introduced with 86-DOS 0.42 in 1981 and carried over into MS-DOS, PC DOS, DR-DOS etc., will overflow at the end of 2107-12-31. The last modification date stamp (and with DELWATCH 2.0+ also the file deletion date stamp, and since DOS 7.0+ optionally also the last access date stamp and creation date stamp), are stored in the directory entry
with the year represented as an unsigned seven bit number (0–127),
relative to 1980, and thereby unable to indicate any dates in the year
2108 and beyond. The API functions defined to retrieve these dates officially only support dates up to 2099-12-31.
This will also affect the Zip archive file format, as it uses FAT file modification timestamps internally.
Year 2137
GPS dates are expressed as a week number and a day-of-week number, with the week number initially using a ten-bit
value and modernised GPS navigation messages using a 13-bit field. Ten
bit systems would rollover every 1024 weeks (about 19.6 years) after
Sunday 6 January 1980 (the GPS epoch), and 13 bit systems rollover every 8192 weeks. 13 bit systems will rollover to zero in 2137.
Year 2262
The Go programming language has a
UnixNano API that counts nanoseconds since 1970 as a 64-bit signed integer.
This value will overflow on 2262-04-11. This is a limitation of similar
nanosecond timekeeping systems, such as the Timestamp object in Python pandas, C++ chrono::system_clock or the QEMU timers.
Year 4501
Microsoft Outlook uses the date January 1, 4501 as a placeholder for "none" or "empty".
Year 10,000
The year 10,000 will be the first Gregorian year with five digits.
Although many people at first consider this year to be so far distant
that a problem of this type will never actually occur, certain classes
of calculations in disciplines such as astronomy and physics already need to work with years of this magnitude and greater. These applications also have to deal with the Year zero problem. All future powers of 10 years have the potential for similar problems.
Year 30,828
Beginning
14 September 30,828, Windows will not accept dates beyond this day and
on startup, Windows will complain about "invalid system time". This is
because the FILETIME value in Windows, which is a 64-bit value
corresponding to the number of 100-nanosecond intervals since 1 January
1601, 00:00:00.0000000 UTC, will overflow its maximum possible value on
that day at 02:48:05.4775808 UTC.
Years 32,768 and 65,536
Programs
that process years as 16-bit values may encounter problems dealing with
either the year 32,768 or 65,536, depending on whether the value is
treated as a signed or unsigned integer.
For the year 32,768 problem, years after 32,767 may be interpreted as negative numbers, beginning with −32,768. The year 65,536 problem is more likely to manifest itself by representing the year 65,536 as the year 0.
Relative time overflow
Microsoft
In
Microsoft Windows 7, Windows Server 2003, Windows Server 2008 and
Windows Vista, TCP connection start information was stored in 1/100ths
of a second, using a 32bit unsigned integer, causing an overflow and TCP
connections to fail after 497 days.
Boeing
The Boeing 787
aircraft has had at least two software issues related to time storage.
In 2015 an error was reported where time was stored in 1/100ths of a
second, using a signed 32-bit integer, and the systems would crash after
248 days. In 2020, the FAA
issued an airworthiness directive for a problem where, if the aircraft
is not powered down completely before reaching 51 days of uptime,
systems will begin to display misleading data.
Far-fetched problems
Certain problematic years occur so far in the future, well beyond the likely lifespan of the Earth, the Sun, humanity, and even past some predictions of the lifetime of the universe,
that they are mainly referenced as matters of theoretical interest,
jokes, or indications that a related problem is not truly solved for any
reasonable definition of “solved”.
- The year 292,277,026,596 (2.9×1011) and 584,554,051,223 (5.8×1011) problems: the years that 64-bit Unix time becomes negative (assuming a signed number) or reset to zero (for an unsigned representation). The year 5,391,559,471,918,239,497,011,222,876,596 (5.4×1030) and 10,783,118,943,836,478,994,022,445,751,223 (1.1×1031) problems: the years that 128-bit Unix time becomes negative (assuming a signed number) or reset to zero (for an unsigned representation).
Note: these year values are based on an average year of exactly 365.2425 days, which matches the 4/100/400 leap year rules of the commonly used Gregorian calendar.
Additional adjustments to the calendar over intervals this long are
unavoidable, as the actual year is currently slightly shorter (about
365.242374 days) than assumed, the length of Earth's orbit around the
Sun changes over time (tropical years are currently becoming shorter at
about 0.53 seconds per century), and in any case, all of these times far
exceed the likely existence of the Earth. So the year numbers should be considered approximate.
Time zone and daylight saving time
Time zones and daylight saving time can cause trouble in computer applications when:
- Communicating between places with different time zones or using the same device in a different time zone
- Daylight saving time starts and ends, especially in the fall when the same time occurs twice
- The time zone in a specific area changes or daylight saving time is adjusted, especially when there isn't enough time for software and firmware to be updated accordingly
- The time shifts less or more than 1 hour forward in the spring
- The start/end dates of summer time depend on other astronomical events
- Daylight saving time is not adopted by everyone in the same place
