- Header (computing)
In
information technology , header refers to supplementaldata placed at the beginning of a block of data being stored or transmitted. Indata transmission , the data following the header are sometimes called the "payload" or "body ".It is vital that header composition follow a clear and unambiguous
specification orformat , to allow forparsing .Examples
* In an
e-mail , the text (body) is preceded by header lines indicating sender, recipient, subject, sending time stamp, receiving time stamps of all intermediate and the finalmail transfer agent s, and much more. (See RFC 2822 for details.)* In a
data packet sent via theInternet , the data (payload) are preceded by header information such as the sender's and the recipient'sIP address es, the protocol governing the format of the payload and several other formats. The header's format is specified in theInternet Protocol .* In data packets sent by
wireless communication , and in sectors of data stored onmagnetic media , typically the header begins with asyncword to allow the receiver to adapt to analog amplitude and speed variations and forframe synchronization .* In
graphics file format s, the header might give information about an image's size, resolution, number of colours, and the like. SeeHTML element .* In
Archive file format s, the file header might serve as afingerprint orsignature to identify the specificfile format and corresponding software utility.* In some
programming language s (for example C andC++ ) the functions are declared inheader file s.ee also
*
Trailer (information technology)
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