Extended Code 39
Code 39 was the first barcode to be able to encode both numbers and letters. It can have a varying length, encoding up to 43 different characters. Extended Code 39 is an updated version of Code 39, which uses combinations of those same encoded characters to allow it to represent the entire range of 128 ASCII characters, including punctuation and special symbols, as well as lower case letters. It is generally used for military and automotive purposes.
Specifications: Extended Code 39 barcodes are set up similarly to regular Code 39 codes, with specially designated start and end characters (represented as * in a regular font), along with an optional check digit, to ensure accuracy. Each special character is represented by a combination of two regular Code 39 characters. This is possible since Code 39 already uses character combinations to represent other characters.
Advantages: Extended Code 39 is more versatile, being able to encode any character you need.
Disadvantages: Since each special character is a combination of two different regular Code 39 characters, it makes the code longer. The more special characters you use, the longer the code will be. In addition, since characters can be read in two different ways (as either two regular characters in Code 39 or one special one in Extended), scanners must be specially configured in order to read an Extended 39 code (as opposed to regular Code 39, which can be read virtually universally). Finally, the check digit is optional, which increases the risk of errors if it is not used.
Code 39 - The predecessor to Extended Code 39, uses the same encoding, but with limited character options.