A JFIF file consists of a sequence of markers or marker segments (for details refer to JPEG, Syntax and structure). The markers are defined in part 1 of the JPEG Standard. Each marker consists of two bytes: an codice_1 byte followed by a byte which is not equal to codice_2 or codice_1 and specifies the type of the marker. Some markers stand alone, but most indicate the start of a marker segment that contains data bytes according to the following pattern: