Abstract: A machine-readable medium and methods of reading and writing same are disclosed. The machine-readable medium comprises a substrate having an array of addressable locations thereon, each addressable location adapted to be physically associated with a collection of non-polymeric molecules. The molecules in each collection are selected from a set of unambiguously identifiable molecules, each molecule uniquely associated with a predetermined position in a numerical value, wherein the presence of the molecule in the collection indicates a predetermined digit at the associated position and the absence of said molecule in the collection indicates a zero at said associated position.