I am currently pseudoparallel reading (i am currently reading one other book) The Pattern On The Stone By Daniel Hillis and i am really really impressed about the simple explanation on logical gates (boolean algebra).
Hillis is using as an example The Tinkertoy computer - the mechanical computer for playing TicTacToe !
Look at this page to take a quick look: The Tinkertoy computer
BTW The first mechanical computer is the The Antikythera mechanism 100BC to predict astronomical positions and eclipses.
Truly Amazing !