The Alphanumeric code corresponds with the position of the tube in the rack (e.g. A1). The code is therefore unique per rack.
A 1D Barcode is the standard 'barcode' (type 128B). With a standard barcode the data that is stored can only be numerical (i.e. a series of numbers). Custom barcodes are available on request and can contain a prefix of three letters or numbers.
The 2D Data-Matrix is an open 2D code and is laser-etched on the bottom of the tube. It consists of a 10-digit number which results in approximately 10 billion different possibilities, guaranteeing (manufacturer) unique codes. Besides the standard 2D Data-Matrix codes, custom 2D Data-Matrix codes are available on request and can contain a prefix of three letters or numbers, resulting in a possible 13-digit code.
For more information on custom coding, fill out the form here