During my time at Waseda university my friend David was (and probably still is) a big Minecraft fan.
This is a simple 8 bit Arithmetic Logic Unit (ALU) that was built using XOR, OR, AND, NOT gates and a multiplexor implemented using ‘redstone circuit’ objects in the game ‘Minecraft’. The unit was able to do simple arithmetic and logical operations on two 8-bit input values by selecting the appropriate Op-codes.

Above is a high level overview of the whole system, main parts are labelled with a number.
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The 'control room' where two 8 bit values are input using in-game 'levers' (on for 1 off for 0), op-codes can be selected using levers and the output is displayed as in game 'lamps'.
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The 8 white buses carrying the input from the control room to the rest of the system, the red and yellow lines you see carry the op-codes which decides where the input will be directed.
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The area where logical operations can be performed on the input.
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The area where addition and subtraction can be performed on the input.
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The green buses that carry the output back to the control room









If you have Minecraft and would like to take a look around for yourself, you can find the world file here
Many thanks to David Doludda who between ourselves have spent too many hours in this game.