Implementing logic gates

The logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels. In most logic gates, the low state is approximately zero volts (0 V), while the high state is approximately five volts positive (+5V). There are seven basic logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR. This article explain and implement AND, OR, NOR and XOR. The AND gate is so named because, if 0 is called "false" and 1 is called "true", the gate acts in the same way as the logical "and" operator. When we use OR gate the output is "true" if either or both of the inputs are "true". If both inputs are "false", then the output is "false". The XOR (exclusive-OR) gate is 1 if the inputs are different, but 0 if the inputs are the same. The NOR gate is a combination OR gate followed by an inverter. The main objective of this article is to verify that the NAND gate is a universal gate. That means that by combining different NAND gates one can obtain another logic gates.
Complete Article:
http://www.roboticproject.net/Article_LogicLabII.html