A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving date and time of day, sometimes accurate to a small fraction of a second. Timestamps do not have to be based on some absolute notion of time, however. They can have any epoch, can be relative to any arbitrary time, such as the power-on time of a system, or to some arbitrary time in the past. A distinction is sometimes made between the terms datestamp, timestamp and date-timestamp: * Datestamp or DS: A date, for example -- according to

ISO 8601 ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the International Organization for Standardization (ISO) and was first published in 1988, with updates in ...

* Timestamp or TS: A time of day, for example :: using

24-hour clock The modern 24-hour clock is the convention of timekeeping in which the day runs from midnight to midnight and is divided into 24 hours. This is indicated by the hours (and minutes) passed since midnight, from to , with as an option to indicate ...

* Date-timestamp or DTS: Date and time, for example --, ::

History

The term "timestamp" derives from

rubber stamp A rubber stamp is an image or pattern that has been carved, molded, laser engraved, or vulcanized onto a sheet of rubber. Rubber stamping, also called stamping, is a craft in which some type of ink made of dye or pigment is applied to a rub ...

s used in offices to stamp the current date, and sometimes time, in ink on paper documents, to record when the document was received. Common examples of this type of timestamp are a

postmark A postmark is a postal marking made on an envelope, parcel, postcard or the like, indicating the place, date and time that the item was delivered into the care of a postal service, or sometimes indicating where and when received or in transit. ...

on a letter or the "in" and "out" times on a

time card Time is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequence events, to compa ...

. With the advent of digital data systems, the term has expanded to refer to digital date and time information attached to digital data. For example,

computer file A computer file is a System resource, resource for recording Data (computing), data on a Computer data storage, computer storage device, primarily identified by its filename. Just as words can be written on paper, so too can data be written to a ...

s contain timestamps that tell when the file was last modified, and

digital camera A digital camera, also called a digicam, is a camera that captures photographs in Digital data storage, digital memory. Most cameras produced today are digital, largely replacing those that capture images on photographic film or film stock. Dig ...

s add timestamps to the pictures they take, recording the date and time the picture was taken.

Digital timestamps

This data is usually presented in a consistent format, allowing for easy comparison of two different records and tracking progress over time; the practice of recording timestamps in a consistent manner along with the actual data is called ''timestamping''. Timestamps are typically used for logging events or in a

sequence of events Time is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequence events, to compa ...

(SOE), in which case each event in the log or SOE is marked with a timestamp. Practically all computer file systems store one or more timestamps in the per-file metadata. In particular, most modern operating systems support the POSIX

stat (system call) is a Unix system call that queries the file system for metadata about a file (including special files such as directories). The metadata contains many fields including type, size, ownership, permissions and timestamps. For example, the ...

, so each file has three timestamps associated with it: time of last access (atime: ls -lu), time of last modification (mtime: ls -l), and time of last status change (ctime: ls -lc). Some

file archiver In computing, a file archiver is utility software that combines computer file, files into a single archive file or in less common cases, multiple files. A minimally designed archiver might concatenate the content of files along with file file n ...

s and some version control software, when they copy a file from some remote computer to the local computer, adjust the timestamps of the local file to show the date/time in the past when that file was created or modified on that remote computer, rather than the date/time when that file was copied to the local computer. Timestamps are often found to be dirty in many cases. Without cleaning up inaccurate timestamps, time-related applications such as provenance analysis or pattern queries are not reliable. To evaluate the correctness of timestamps, temporal constraints can be applied, declaring distance limits between timestamps.

Standardization

standardizes the representation of dates and times. These standard representations are often used to construct timestamp values.

Examples

Examples of date-timestamps: * Thurs 12/31/2009 1:35 p.m. — mixed-endian date, big-endian 12-hour clock * Thurs 31.12.2009 13:35 — same time as the above, different format with little-endian date and big-endian 24-hour clock * 2005-10-30 T 10:45

UTC Coordinated Universal Time (UTC) is the primary time standard globally used to regulate clocks and time. It establishes a reference for the current time, forming the basis for civil time and time zones. UTC facilitates international communica ...

—

international order (

big-endian '' Jonathan_Swift.html" ;"title="Gulliver's Travels'' by Jonathan Swift">Gulliver's Travels'' by Jonathan Swift, the novel from which the term was coined In computing, endianness is the order in which bytes within a word (data type), word of d ...

) with

time zone A time zone is an area which observes a uniform standard time for legal, Commerce, commercial and social purposes. Time zones tend to follow the boundaries between Country, countries and their Administrative division, subdivisions instead of ...

) * 2007-11-09 T 11:20 UTC — same format as the above, hence easy to compare and perform alphanumeric sorting * Sat Jul 23 02:16:57 2005 * 2009-10-31T01:48:52Z —

* 2009-10-31 01:48:52Z — "Internet time" per

RFC 3339 ISO 8601 is an international standard covering the worldwide exchange and communication of date and time-related data. It is maintained by the International Organization for Standardization (ISO) and was first published in 1988, with updates in ...

, based on ISO 8601 * 1256953732 —

Unix time Unix time is a date and time representation widely used in computing. It measures time by the number of non-leap seconds that have elapsed since 00:00:00 Coordinated Universal Time, UTC on 1 January 1970, the Unix Epoch (computing), epoc ...

, equivalent to 2009-10-31 T 01:48:52Z * 1969-07-21 T 02:56 UTC * 07:38, 11 December 2012 (UTC) * 1985-102 T 10:15 UTC — year 1985, day number 102, ''i.e.'', 1985 April 12 * 1985-W15-5 T 10:15 UTC — year 1985, week number 15,

weekday The weekdays and weekend are the complementary parts of the week, devoted to labour and rest, respectively. The legal weekdays (British English), or workweek (American English), is the part of the seven-day week devoted to working. In most o ...

5 = 1985 April 12 * 20180203073000 — used in

Wayback Machine The Wayback Machine is a digital archive of the World Wide Web founded by Internet Archive, an American nonprofit organization based in San Francisco, California. Launched for public access in 2001, the service allows users to go "back in ...

memento

URL A uniform resource locator (URL), colloquially known as an address on the Web, is a reference to a resource that specifies its location on a computer network and a mechanism for retrieving it. A URL is a specific type of Uniform Resource Identi ...

s, equals 3 February 2018 07:30:00 Examples of datestamps: * 2025-05-25 —

international representation of 2025 May 25 Examples of timestamps: * 17:30:23 — time of day in an afternoon * 123478382 ns — the number of nanoseconds since boot * 17 minutes — an arbitrary minute counter that increments every 1 minute since its last manual "reset" event Sequence number: * 21 — a unitless counter that indicates only the relative order of events; this is event #21, which comes after 20 and before 22

References

{{Authority control Time

History

Digital timestamps

Standardization

Examples

See also

References