Computronium

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

It also refers to a theoretical arrangement of matter that is the best possible form of computing device for that amount of matter.

In the Hitchhiker's Guide to the Galaxy books, by Douglas Adams, the entire Earth is portrayed as programmable matter; a computer designed to find the question to the Answer to Life, the Universe, and Everything.

Greg Egan uses the term in Zendegi.

In the Revelation Space books, by Alastair Reynolds, a neutron star called Hades is converted into a massive super computer. The neutronium substance of Hades would therefore be computronium.

In Orion's Arm Universe Project computronium is any form of matter which supports computation, including the human brain.

In Charles Stross and Cory Doctorow's book, The Rapture of the Nerds, the Sun is surrounded by Dyson spheres of computronium, which host the Singularity.