When compared with dot blots and Southern blots, microarrays represent high-density minatur­ized arrays of molecular samples, facilitating the screening of genomic DNA or cDNA samples for the presence of one in 1,00,000 or more DNA sequences. The technology involves hybridization of an unknown sample to an ordered array of immobilized molecules of known sequences.
This produces a specific hybridization pattern that can be analysed or compared to a given standard sometimes with the help of computer devices. These microarrays can be prepared either by the synthesis of oligonucleotides on a DNA chip or by deposition of available DNA sequences (e.g. PCR products, cloned DNA fragments) on such a chip.

Miniaturization of conventional assays (as in Southern blots for RFLP) is a general trend in molecular biology, since micro scale assays raduce reagent consumption, minimize reaction volumes, increase the sample concentration and accelerate the reaction kinetics. Although the initial microarray assays focused on nucleic acid hybridization, future studies will certainly involve parallel analysis of proteins, lipids, carbohydrates and other small molecules. For instance, protein chips have already become available for the study of proteins.