A history of DNA microarrays (arrays were first created as macro arrays in the mid-1980s) covers the a brief explanation of the effects of genes on disease, related papers published in 2002 and 2003, types of microarrays, the process, alternative approaches with microarrays, and the past, present, and future of microarrays. The first arrays were used primarily for DNA clones, PCR products, or oligonucleotides used with radioactively-labeled targets. Microarrays were created through the use of pin spotters, or pin-based robotic systems that can dispense a precise volume of a DNA solution in a spot sized at about 150 microns onto a glass slide. Further developments and uses are described that led to currently available microarrays, which use templates for genes of interest that are obtained and amplified by PCR, purified and exposed to quality control, and printed with aliquots of approximately 5 nL on coated glass microscope slides. Affymetrix's and Agilent's processes and techniques are highlighted. Commercially produced microarrays have the advantages of quality and uniformity of arrays. Alternative approaches are used by Nanogen (which developed an electronic microarray that uses the natural charge of DNA molecules) and Applied Biosystems (which developed a chemiluminescence system). These methods overcome the use of high-cost fluorescent dyes. Advanced technologies include Agendia of the Netherlands use of Agilent technology to profile almost 300 patients for 70 gene prognosis profiles or comparative genomic hybridization (CHG). With CGH, researchers look directly at genomic DNA instead of the expression profile of RNA. CGH allows direct measurement of the copy number of a given gene, which is important in cancer research because direct measurement permits faster chromosome mapping.