Timestamp

A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving the 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 some arbitrary time in the past. A distinction is sometimes made between the terms datestamp (DS), timestamp (TS) and date-timestamp (DTS): * Datestamp: A date, for example - - according to ISO 8601 * Timestamp: A time of day, for example : : (using the 24-hour clock) * Date-timestamp: Date and time, for example - - T : : (ISO 8601)

A timestamp is a sequence of characters or encoded information identifying when a certain event occurred, usually giving the 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 some arbitrary time in the past. A distinction is sometimes made between the terms datestamp (DS), timestamp (TS) and date-timestamp (DTS): Datestamp: A date, for example - - according to ISO 8601 Timestamp: A time of day, for example : : (using the 24-hour clock) Date-timestamp: Date and time, for example - - T : : (ISO 8601) ==Digital timestamps== Timestamps are usually presented in a consistent format, allowing for easy comparison of multiple records and the tracking progress over time; the practice of recording timestamps in a consistent manner along with the actual data is called timestamping. Timestamps are frequently used for logging events or in a sequence of events (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), whereby 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 ). When some file archivers and version control systems copy a file from a remote computer to the local computer, they adjust the timestamps of the local file to show the date/time in the past when that file was created or modified on the 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== ISO 8601 standardizes the representation of dates and times. These standard representations are often used to construct timestamp values. 1985-W15-5 T 10:15 UTC — year 1985, week number 15, weekday 5 = 1985 April 12 20180203073000 — used in Wayback Machine memento URLs, equals 3 February 2018 07:30:00 Examples of datestamps: 2025-05-25 — ISO 8601 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 ==See also== Advanced electronic signature Backdating and forward dating, signing a document with a timestamp (sometimes legitimately) representing a point in time either forwards or backwards Bates numbering Decentralized trusted timestamping on the blockchain Sequence number, consecutive number in a sequence of numbers, for example used in sorting Linked timestamping Timestamping (computing) Timestamp-based concurrency control Trusted timestamping ==References==

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