Base-pairing (i.e., A-T and G-C for DNA; A-U and G-C for RNA) and hybridization is the underlining basis of DNA microarrays. Its principle is the matching of known and unknown DNA samples on base-pairing rules and automating the process of identification of the unknowns. An array experiment can make use of common assay systems such as microplates or standard blotting membranes, and can be created manually or make use of robotics to deposit the sample. Macroarrays contain sample spots of about 300 microns or larger and can be easily imaged by existing gel and blot scanners. Microarrays usually have thousands of spots that are less than 200 microns in diameter. They require specialized robotics and imaging equipment that generally are not commercially available as a complete system.