Computronium is the arrangement of physical resources optimized for its use as a computing substrate.
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An attempt to estimate the upper limits of computation.
Lloyd, Seth (2000) Ultimate physical limits to computation, Nature, vol. 406, pp. 1047–1054.
Sandberg, Anders (2018) Answer to 'Computronium and time dilation and Bremermann’s limit', Stack Exchange, May 23.