Logic gates perform a boolean operation - they process signals which represent true or false. Normally the positive supply voltage +Vs represents true or 1 and 0V represents false or 0. Other terms which are used for the true and false states are On and Off, and Hi and Lo.There are many different type of gates but for this disucssion we will look at 5: AND - both input conditions must be true for output to be true, OR - either input condition can be true for output to be true, NOT - simply inverts the input, NAND - an AND gate with an inverter, and NOR - an Or gate with an inverter.