Header (computing)

Header is a technical term in information technology.

When storing or transmitting data it is often necessary to suplement the data with additional information for the process of handling the data. If this additional information is placed at the beginning of the data it is called a header. In case of information transmission the actual data is sometimes called the payload or the body.

It is vital that a header follows a clear specification or format to allow for parsing it.

Examples

• In an e-mail the text of the e-mail (the said "body") is preceded by lines indicating sender, recipient, subject, sending time stamp, receiving time stamp of all intermeidate and the final mail server and much more. (See RFC 822 for details.)

• In a data packet sent through the internet the data (payload) is preceded by information like the sender's and the recipient's IP address, the protocol governing thr format of the payload and several other formats. The format is specified in the internet protocol.

• In graphics formats the header might give information about resolution, number of colors and the like.