Code 39 can be said to represent the standard barcode symbology (it is also known as code 3 of 9). Three of the nine elements (bars and spaces) for each character are wide and six elements are narrow. In order to encode information (say 'ABCD'), it is necessary to start the code with a start character and end it with a stop character. The symbol '*' is used for this purpose in code 39. In order to print a barcode for ABCD, it would thus be necessary to enter *ABCD*. To the left and right of the code there need to be so-called 'quiet zones' of at least 6.5 mm in width so that a scanner or reader can recognise where the barcode begins and ends.
Other forms of barcode employ a similar system. Each of the symbols of the UPC/EAN barcodes has four bars and spaces of different widths, as do the symbols of code 128. Code 39 can be used to represent a total of 39 characters (numerals 0 - 9, 26 letters and 7 special characters). Each character is represented by a 3 or 9 bar/space combination in which these are of two different widths.
Barcodes that do not use a check digit (such as code 39, code 93, codabar and 2 of 5 industrial) can be entered directly in the target application and formatted in the corresponding barcode form. Barcodes with interleaving or check digits require a specific programme for calculation. The calculated barcodes can then be fed from the intermediate system into the target application.