From the Wikipedia entry on Revelation Space universe technology:

http://en.wikipedia.org/wiki/Technology_in_Revelation_Space

"Cryo-arithmetic engines are a specific class of quantum computer discovered by the Conjoiners. When certain algorithms are executed on processors of this architecture, it leads to a local violation of the Second law of thermodynamics: the computer gets colder instead of hotter. Consequently, cryo-arithmetic engines have massive industrial (as opposed to computation...