A nanocomputer is a computer whose physical dimensions are microscopic. The field of nanocomputing is part of the emerging field of nanotechnology. Several types of nanocomputers have been suggested or proposed by researchers and futurists.
Electronic nano-computers will work in a similar way to the way current microcomputers work. The main difference is a physical scale. More and more transistors are squeezed on silicon chips with each passing year; attest to the evolution of integrated circuits (ICs) capable of increasing storage capacity and processing power. The maximum limit to the number of transistors per unit volume is imposed by the atomic structure of matter. Most engineers agree that technology has not come close to this limit. In the electronic sense, the term nano-computer is relative. By the standards of the 1970s, today's ordinary microprocessors could be called nanodevices.
Chemical and biochemical nano-computers would store and process information in terms of chemical structures and interactions. Biochemical nano-computers already exist in nature; are manifest in all living beings. But these systems are largely uncontrollable by humans. We can not, for example, program a tree to calculate the digits of pi, or program an antibody to fight a particular disease (although medical science has approached this ideal in the formulation of vaccines, antibiotics and antiviral drugs). The development of a true chemical nano-computer will probably proceed along lines similar to genetic engineering. Engineers should figure out how to get individual atoms and molecules to perform controllable calculations and data storage tasks.
Mechanical nanocomputers would use tiny moving components called nanogears to encode information. Such a machine resembles Charles Babbage's analytical engines of the nineteenth century. For this reason, mechanical nanocomputer technology has provoked controversy; some researchers consider it unfeasible. All the problems inherent in Babbage's apparatus, according to opponents, are magnified a million times in a mechanical nanocomputer. However, some futurists are optimistic about technology, and have even proposed the evolution of nanorobots that could operate, or be controlled by, mechanical nanocomputers.
A quantum nano-computer would work by storing data in the form of atomic or spin quantum states. Technology of this type is already under development in the form of single-electron memory (SEM) and quantum dots. The energy state of an electron within an atom, represented by the energy level of the electrons or the shell, can theoretically represent one, two, four, eight or even 16 bits of data. The main problem with this technology is instability. Instantaneous electron energy states are difficult to predict and even more difficult to control. An electron can easily fall into a lower energy state, emitting a photon; on the other hand, a photon colliding with an atom can cause one of its electrons to jump into a higher energy state.