A datamatrix barcode is a two dimensional barcode. Two dimensional barcodes outperforms one dimensional barcodes on several fronts. The first, obvious reason is of course the amount of information that can be stored.
The other reasons are less obvious. One dimensional barcodes sought to increase their storage capacities by firstly, increasing the number of variations of bar thickness; and secondly, by reducing the width of their minimum module widths.
Increasing the number of different possible module widths requires the scanner to distinguish barcode features accurately at high resolution. Reducing the minimum module widths requires even higher resolution on the part of the scanner. For many laser barcode scanners, this limit is 0.005inch, or 0.127mm.
The datamatrix barcode has only one module width for the scanner to distinguish. A module does not even need to be square. In the example above, datamatrix modules can even be round.
There is also no constraint to the datamatrix reader; a datamatrix barcode can be as large as the flat roof top of a building, or small enough to fit an integrated circuit package.
Machined aluminum provides the bright and dark portions by reflecting light differently when viewed from different angles.