header (HDR)

The term header is always used for a header. This can be the initial data field of a data packet or the initial data record for identifying CD data blocks or other files.

1. The header( HDR) is the header part of a data packet to be transmitted. Depending on the protocol, the first data field is the preamble with the bit pattern for synchronization.
   

   Basic structure of a data packet

   This is followed by various administrative and control information such as flags or start frames, the address fields for the destination address and the source address, identification information, packet numbers, the data fields for the packet status and the protocol version, and various other data fields. The user data is not part of the header.
2. When data blocks are marked on compact discs (CDs) or DVDs, the initial identifier, the header, consists of 4 bits, each at the beginning of a data block on the CD-ROM. The header field contains the sector address and the recording method.
3. In graphic files, the header contains the most important information about the graphic, its file format and file size, the image format with the image height and width, the color depth and image compression, and more. Which data the header contains depends on the file format.