Code 39

Code 39 is a barcode symbology that can encode uppercase letters (A through Z), digits (0 through 9) and a handful of special characters like the $ symbol. The barcode itself does not contain a check digit (in contrast to Code 128, for example), but it can be considered self-checking on the grounds that a single erroneously-interpreted bar cannot generate another valid character.

A serious drawback of Code 39 is its low data density; it requires more space to encode data in Code 39 than Code 128. This means that very small items can't be labeled with a Code 39-based barcode. However, Code 39 is still widely used and can be decoded by virtually any barcode scanner/reader.

One advantage of Code 39 is that since there is no need to generate a check digit; it can be integrated easily into an existing printing system by adding a barcode font to the system or printer, then printing the raw data in that font.

Code 128

Code 128 is a high-density barcode symbology. (A special version of it called GS1-128 is used extensively worldwide in shipping and packaging industries.) Code 128 is used for alphanumeric or numeric-only barcodes and it can encode all 128 ASCII characters. This code also incorporates a check digit.

Data Matrix

A Data Matrix code is a two-dimensional matrix barcode consisting of Black-and-White cells or modules arranged in either a square or rectangular pattern. The information to be encoded can be text or raw data. Usual data size is from a few bytes up to 2 kilobytes. The length of the encoded data depends on the symbol dimension used. Error correction codes are added to increase symbol strength: even if they are partially damaged, they can still be read. A Data Matrix symbol can store up to 2,335 alphanumeric characters.