Nano-technology is based on microscopic mechanical cell-like units which replicate rather than multiply. Living organisms multiply, whereas nanites or nanocites are molecular devices that take atomic particles from their environment and use them to make more of themselves. On Earth, nano-technology has been studied for application in medicine, for example creating artificial immune systems or manipulating DNA.
SG-1 has encountered many examples of nano-technology in use on other worlds. On Argos, Pelops had created a nano-virus among the Chosen, shortening a lifespan to approximately 100 days. The Orbanians use a system of nanites injected into the brain as an artificial means of acquiring knowledge. A form of nano-technology was used to artificially accelerate the initial aging of Shifu, the Harsesis child, and Dr. Keffler later applied that same technology on Earth to create Anna. Reese's creator used nano-technology to create an incredibly sophisticated and lifelike artificial life-form, and Reese used the same technology to create the building blocks from which the Replicators are made. The Replicators themselves studied Reese's design and assimilated the nano-technology, enabling them to evolve into human form, composed of millions of microscopic cell units similar to nanites.