Two types: 1.) Discrete: Characters in discrete symbologies are composed of n bars and n − 1 spaces.
Space between bars does not convey information. The width of the spaces does not matter as long as it can't be confused with the end of the message.
2.) Continous Characters in continuous symbologies are composed of n bars and n spaces, and usually abut, with one character ending with a space and the next beginning with a bar, or vice versa. A special end pattern that has bars on both ends is required to end the code.
two types: 1.) A two-width, also called a binary bar code, contains bars and spaces of two widths, "wide" and "narrow". The precise width of the wide bars and spaces is not critical; typically it is permitted to be anywhere between 2 and 3 times the width of the narrow equivalents. 2.) Bars and spaces in many-width symbologies are all multiples of a basic width called the module; most such codes use four widths of 1, 2, 3 and 4 modules.
CODE 39 Code39 barcodes (or Code 3 of 9) are used to label goods across many industries.
It allows the use of both digits and characters, and its name originates in the fact that it could only encode 39 characters
Code 39 (also known as Alpha39, Code 3 of 9, Code 3/9, Type 39, USS Code 39, or USD-3) is a variable length, discrete barcode symbology.