Timestamp

A timestamp is a numerical value representing the number of time units (often seconds) that have elapsed since a reference date called Epoch, the value of which is set to 0.

Calculating a timestamp involves measuring the number of time units that have elapsed since a reference date, the Epoch.

In most systems (Unix, Linux, macOS, Java, PHP, C++), the Epoch is January 1, 1970, at 00:00:00 UTC, and each passing second increments the timestamp by one unit.

A timestamp is used to reliably compare dates by manipulating numbers instead of complex calendar values.

This avoids ambiguities related to daylight saving time changes (when 2:59 a.m. plus one minute becomes 2:00 a.m.) or time zones.

A timestamp can also be used to order events, measure durations, or synchronize computer systems.

Converting a timestamp involves adding the timestamp value to the Epoch date, taking into account the desired time zone.

dCode converter interprets the number of seconds elapsed since the Epoch and automatically calculates the year, month, day, hour, minute, and second to obtain the corresponding date in UTC or local time.

Each software or system/hardware clock environment can use its own Epoch, as well as a different unit of time.

Here are the most common Epochs:

— Unix, Linux, macOS, most languages (C, C++, PHP, MySQL, Python, etc.): January 1, 1970 at 00:00:00 UTC (seconds; some configurations allow for milliseconds or microseconds).

— JavaScript: January 1, 1970 at 00:00:00 UTC, but in milliseconds.

— GPS: January 6, 1980 at 00:00:00 UTC, with counting in weeks plus seconds (and a rollover every 1024 weeks).

— Windows (since NT): January 1, 1601 at 00:00:00 UTC, in units of 100 nanoseconds.

— .NET: January 1, 0001 at 00:00:00, in 100-nanometer ticks.

— PostgreSQL: January 1, 2000 at 00:00:00 UTC.

To convert a UTC timestamp to local time, add the time zone offset, including any seasonal time changes. The conversion is performed using the formula: Local Date = UTC Date + Time Zone Offset.

The dates in Excel have their own Epoch (January 0, 1900 or December 31, 1899), the trick is to remove the one from Unix.

To convert a Unix timestamp to an Excel date, divide the timestamp by 86400 to express it in days, then add the Unix epoch.

January 1, 1970, at 00:00:00 UTC was chosen as the Epoch for Unix to simplify time calculations in early versions of the system and to provide a consistent international reference point.

This date is considered to mark the beginning of the UNIX era.

On January 19, 2038, at 03:14:07 UTC, the Unix timestamp will reach the maximum value representable by a 32-bit signed integer (2^31 - 1 = 2147483647).

The next second, the expected value (2147483648) will be interpreted as a negative number, referring to December 13, 1901.

This overflow will cause a malfunction on systems still using a 32-bit format.

Modern 64-bit systems, however, are not affected by this problem.