Evolution of AND Gate.

Logic Gates are the basics of Digital electronics. To your surprise. AND gate was developed using Diodes as the elements.
Here is the AND gate using DIode diode logic

AND gate 

when one input is low. The diode in the path gets Forward biased.
So the diode forward voltage is the output.

Same for 0 0

               0 1

When both the inputs are 5 volts. both Diodes are REverse biased.So output is High

http://www.youtube.com/watch?v=Sn6pV4cMZ4c