time stamp

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Time stamp with date display and date imprint, ERFU brand, around 1960. Mechanical clockwork, manual winding, eight days running time
A timestamp on a letter

A time stamp ( English time stamp ) is used to an event a unique timing assigned.

An example of this is the postmark on letters, although their accuracy normally only relates to the day (seldom - especially in the banking sector - even in the hour range ). Displayed time displays for photos and video recordings are also known as time stamps. These stamps on paper can hardly be changed or separated from the document. On the other hand, not every logged time specification is a time stamp, especially not if the time specification can be easily changed or is unreliable.

A digital time stamp has a defined format according to its application. It should be forgery-proof, since the time stamp should be used to prove the times of events.

Digital time stamps are certificates that an electronic document (or the hash value of this document) was available to the issuer of the time stamp at the specified time. They complement the use of electronic signatures in legal transactions. Courts can electronically confirm that a message has arrived on time. Archives can thus prove that a document has not been changed since it was archived. Even with large tenders, time stamps are used to document and secure the offers.

The German Signature Act regulates the requirements for the issuance of qualified time stamps as a particularly high-quality form of such a certificate, which ensures that the valid legal time has been recorded and for which forgeries and falsifications are excluded. With the procedures used today, the issuer of a qualified time stamp as an uninvolved third party signs the hash value of the certified document together with the current time (date and time) with a qualified electronic signature . The Time Stamp Protocol ( RFC 3161 ) regulates the transmission of information from a time stamp service on the Internet.

In modern, computerized communications and data technology, due to the globally different time zones and thus possible misunderstandings, time stamps are either generally given in the coordinated world time UTC or supplemented with information that shows the local deviation from the world time zone. This means that time stamps can be correctly converted into different local times.

Differences in the times

For the universal use of a time stamp with local time (e.g. in an e-mail) it is important to add the indication of the offset to UTC as a numerical specification or by name such as CET or MEST. This is also required in ISO 8601 . This is the only way to achieve a complete comparison of time stamps and to calculate time differences between two time stamps. This is an important requirement, particularly in IT systems that process data from several continents.

Depending on the context, time information relates to different time systems or types of clocks : If a reference to "reality" is important, the value of a real-time clock is used . If, on the other hand, only the order (or the causal order - see also Happened-Before ) of the events is important, a logical clock is used . In the simplest case this is a counter or a sequence number .

However, if more than two parties are involved in the communication (i.e. there are more than two places where events can occur), it is necessary to use a more complex logical clock, such as a Lamport clock or vector clocks : They make it possible to determine the causal order of the events without the (real-time) clocks at the different locations having to be exactly synchronized . Such logical clocks are mainly used by network protocols and transaction systems .

Time information in file systems

The FAT file system uses the system time with an accuracy of 2 seconds for time information . The most widespread type of time stamp in file systems is probably Unix time , which indicates the number of seconds since January 1st, 1970 00:00 UTC without leap seconds . The standardized Unix file times make it much easier to network remote Unix computers and their file systems on the Internet. Systems that inadequately encode this number as a signed 32- bit number are expected to have a year 2038 problem on January 19, 2038 . A time resolution in microseconds is not uncommon on computers today. The Intel - microprocessors was from the Pentium the so-called time stamp counter (. English Time Stamp Counter ) integrated. This can be read out with the assembler command RDTSC. When synchronizing file systems there are problems under Windows because NTFS and FAT resolve the time with different degrees of accuracy.

Output of time information on a computer with time zone Europe / Berlin

With PHP , the time can be displayed as follows:

echo time();
// Unix-Zeit-Information des aktuellen Datums, z. B. 1214617821

echo mktime(0, 31, 30, 02, 14, 2009);
// ergibt: 1234567890
// Am Samstag, 14.02.2009 00:31:30 MEZ war die Zeit genau 1234567890

With Visual Basic , times can be displayed as follows:

Dim jetzt As Date = Date.Now
' ergibt: 633702174022502000

Dim jetzt As Date = #2/14/2009 12:31:00 AM#
' ergibt: 633701682600000000

Using C # , a time can be displayed as follows:

System.DateTime jetzt = System.DateTime.Now;
// ergibt: 633702174022502000

System.DateTime jetzt = 14/02/2009 00:31:00;
// ergibt: 633701682600000000

With Ada a time can be displayed as follows:

with Ada.Calendar; use Ada.Calendar;
with GNAT.Calendar.Time_IO;

procedure currenttime is
   Now : Time := Clock;
   GNAT.Calendar.Time_Io.Put_Time (Now, "%s");
   -- Achtung! Ada-Zeit beginnt 1970-01-01  00:00:00 UTC

Timestamp on Youtube

With YouTube videos, the precise focus on individual scenes is possible via the URL that can be selected to the second .

See also

Web links

Commons : Timestamp  - collection of images, videos and audio files
Wiktionary: Timestamp  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. Youtube links accurate to the second C't November 20, 2010
  2. Create a YouTube link with a time stamp - this is how it works , by Hannah Becker Chip (magazine) February 24, 2014
  3. Create Internet YouTube link with timestamp - that's how it works , by Isabelle Bauer, Heise.de July 12, 2019