Timestamp

A timestamp (English timestamp) is used to assign an event a unique point in time. An example is the postal stamp on letters, although their accuracy is normally only on the day (rare - even within hours - especially in the banking sector ) applies. Also Displayed time displays with photos and video recordings are referred to as a time stamp. These stamps on paper can hardly be changed or disconnected from the document. On the other hand, not every logged time stamp, a time stamp, especially not when the time specification can be easily modified or unreliable done.

A digital time stamp has its application in accordance with a defined format. He should be executed to forge because time points are to be detected events with the time stamp.

Digital time stamps are certificates that has an electronic document ( or its hash up of this document) at the specified time presented to the exhibitor of the timestamp. They complement the use of electronic signatures in legal relations. Courts can thus confirm the timely arrival of a message electronically. Archives can prove so that a document since the archiving was not changed. Even with large tenders timestamps are used as evidence and securing the most popular. The German signature law specifies the requirements for the issuance of qualified time stamps as a particularly high-quality form of such a certificate, in which it is ensured that the applicable statutory period was recorded, and where counterfeiting and falsification are excluded. In the methods used today the issuer of a qualified timestamp signs on as uninvolved third parties the hash value of the certified document along with the current time stamp ( date and time) with a qualified electronic signature. The Time -Stamp Protocol (RFC 3161) regulates the transmission of information of a time stamping service on the Internet.

In the modern, computerized messages and data technology timestamps are either generally indicated because of the global time zone differences and thus avoid possible misunderstandings in the Coordinated Universal Time UTC or supplemented with an indication which indicates the local deviation to the world time zone. This timestamp can be converted correctly into different local times.

Differences in the times

Important for the universal use of a time stamp with local time (for example in an e -mail) is the addition to specifying the offset to UTC as a numeric representation, or by name as CET or MEST. This is also required in ISO 8601. Only then can a full comparison of timestamps be realized and calculating time differences between two timestamps is possible. Especially in computer systems that process data from several continents, this is an important requirement.

Depending on the context, time specifications refer to different time systems and types of watches: Is that a reference to " reality " is important, so we used the value of a real-time clock. If, however, only the order (or the causal order - see also Happened Before ) of the events important to use a logical clock. In the simplest case, this is a counter or a sequence number. But if more than two parties involved in the communication ( ie, there are more than two places where events may occur ), it is necessary to use a more complex logical clock, such as a Lamport clock or vector clocks: you make it possible to determine the causal order of events without the ( real-time ) clocks must be synchronized exactly at the various locations. Such logical clocks are mainly used by network protocols and transaction systems.

Time information in file systems

The famous FAT file system uses for times local time with an accuracy of 2 seconds. The most widespread type of timestamps in file systems is probably the Unix time, which indicates the number of seconds since January 1, 1970 00:00 UTC clock (without leap seconds ). The standard Unix file - times substantially facilitate networking away standing Unix computer and its file systems over the Internet. For systems that encode this number insufficient as a signed 32 -bit number, the year -2038 problem is feared on 19 January 2038. A time resolution of microseconds is now not uncommon on digital computers. The Intel microprocessors (English Time Stamp Counter ) was integrated from the so-called Pentium timestamp counter. This can be read with the RDTSC assembler instruction. When syncing file systems, it comes with Windows problems because NTFS and FAT resolving time with different accuracy.

Output time information on a computer with a Time Zone Europe / Berlin

With PHP, the time can be displayed as follows:

With Visual Basic times can be displayed as follows:

Dim now As Date = Date.Now Console.WriteLine ( jetzt.Ticks ) 'Results: 633702174022502000 Dim now As Date = # 2/14/2009 12:31:00 AM # Console.WriteLine ( jetzt.Ticks ) 'Results: 633701682600000000 With C # is a time can be displayed as follows:

System.DateTime now = System.DateTime.Now; Console.WriteLine ( jetzt.Ticks ); / / Yields: 633702174022502000   System.DateTime now = 14/02/2009 00:31:00; Console.WriteLine ( jetzt.Ticks ); / / Yields: 633701682600000000 With Ada a time can be displayed as follows:

With Ada.Calendar; Use Ada.Calendar; with GNAT.Calendar.Time_IO;   procedure current time is     Now: Time: = Clock; begin     GNAT.Calendar.Time_Io.Put_Time (Now, "% s ");     - Warning! Ada begins 1970-01-01 00:00:00 UTC end; see also

• Distributed systems
• Time clock
• Timecode