Editing Unix time (section)

== Limitations ==
Unix time was designed to encode calendar dates and times in a compact manner intended for use by computers internally. It is not intended to be easily read by humans or to store timezone-dependent values. It is also limited by default to representing time in seconds, making it unsuited for use when a more precise measurement of time is needed, such as when measuring the execution time of programs.<ref name="adv-unix">{{cite book |last1=Rochkind |first1=Mark |title=Advanced UNIX Programing |date=2004 |publisher=Addison-Wesley |isbn=978-0-13-141154-8 |pages=56–63 |edition=2nd}}</ref> 

=== Range of representable times ===
{{see also|Year 2038 problem}}

[[File:Year 2038 problem.gif|thumb|upright=1.8|An animated visual of the [[Year 2038 problem|32-bit Unix time overflow which will occur in 2038]]]]

Unix time by design does not require a specific size for the storage, but most common implementations of Unix time use a [[signed integer]] with the same size as the [[Word (computer architecture)|word size]] of the underlying hardware. As the majority of modern computers are [[32-bit]] or [[64-bit]], and a large number of programs are still written in 32-bit compatibility mode, this means that many programs using Unix time are using signed 32-bit integer fields. The maximum value of a signed 32-bit integer is {{nowrap|2{{sup|31}} &minus; 1}}, and the minimum value is {{nowrap|&minus;2{{sup|31}}}}, making it impossible to represent dates before 13 December 1901 (at 20:45:52 UTC) or after 19 January 2038 (at 03:14:07 UTC). The early cutoff can have an impact on databases that are storing historical information; in some databases where 32-bit Unix time is used for timestamps, it may be necessary to store time in a different form of field, such as a string, to represent dates before 1901. The late cutoff is known as the [[Year 2038 problem]] and has the potential to cause issues as the date approaches, as dates beyond the 2038 cutoff would wrap back around to the start of the representable range in 1901.{{r|adv-unix|p=60}}

Date range cutoffs are not an issue with 64-bit representations of Unix time, as the effective range of dates representable with Unix time stored in a signed 64-bit integer is over 584 billion years, or 292 billion years in either direction of the 1970 epoch.{{r|adv-unix|p=60-61}}<ref>{{cite web |last1=Saxena |first1=Ashutosh |last2=Rawat |first2=Sanjay |title=IDRBT Working Paper No. 9 |url=http://www.idrbt.ac.in/publications/workingpapers/Working%20Paper%20No.%209.pdf |archive-url=https://web.archive.org/web/20120513133703/http://www.idrbt.ac.in/publications/workingpapers/Working%20Paper%20No.%209.pdf |archive-date=13 May 2012 |url-status=dead}}</ref>