computronium

Computronium is a material hypothesized by Norman Margolus and Tommaso Toffoli of the Massachusetts Institute of Technology (MIT) in 1991 to be used as "programmable matter", a substrate for computer modeling of virtually any real object.

It also refers to an arrangement of matter that is the best possible form of computing device for that amount of matter. In this context, the term can refer both to a theoretically perfect arrangement of hypothetical materials that would have been developed using nanotechnology at the molecular, atomic, or subatomic level (in which case this interpretation of computronium could be unobtainium), and to the best possible achievable form using currently available and used computational materials.