From The Escapist:
Last October, I showed you guys a simple CPU that a user named "theinternetftw" created in Minecraft that used torches to ignite redstone wires to add numbers and output that information as binary code. Now, a Minecraft player known as Salaja has created an even more complex machine that is capable of loading 16 lines of code into its RAM, and then performing operations before displaying the results on a screen in hexadecimal notation. In one example video, Salaja loads the "division program" and then successfully divides 9 by 5. The only downfall is that the computation takes a little while for the charge on the redstone to travel, but Salaja's home-designed computer within a computer game is still quite a mind-boggling feat.In related news, people who perform these sorts of feats in Minecraft scare the living shit out of me. Thanks to Greg B. for the tip.
The CPU built with redstone circuitry can load code into its RAM and even print results on a screen.